diff --git a/bin/generate_changes.php b/bin/generate_changes.php
index afea77d..f0e4517 100644
--- a/bin/generate_changes.php
+++ b/bin/generate_changes.php
@@ -1,6 +1,6 @@
 <?php
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\Template\Generator;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Generator\Generator;
 
 require_once \dirname(__DIR__) . '/vendor/autoload.php';
 
diff --git a/docs/content/query/schema.md b/docs/content/query/schema.md
index 54bf979..8f26b9a 100644
--- a/docs/content/query/schema.md
+++ b/docs/content/query/schema.md
@@ -105,6 +105,86 @@ transaction started. For now, only PostgreSQL will benefit from a real database
 transaction.
 :::
 
+### Basic transaction
+
+Considering the API is fluent and all methods can be chained, here is an example
+of a simple table creation:
+
+```php
+$schemaManager
+    ->modify(database: 'my_database')
+        ->createTable(name: 'user')
+            ->column(name: 'id', type: 'serial', nullable: false)
+            ->primaryKey(['id'])
+            ->column(name: 'enabled', type: 'bool', nullable: false, default: 'false')
+            ->column('email', 'text', true)
+            ->uniqueKey(columns: ['email'])
+            ->index(columns: ['email'])
+        ->endTable()
+    ->commit()
+```
+
+:::warning
+Because API may evolve and add new parameters to builder functions, it is recommended
+to use argument naming when using the builder.
+:::
+
+You may also simply issue direct statements, considering the manipulated table already
+exists in your schema:
+
+```php
+$schemaManager
+    ->modify(database: 'my_database')
+        ->column(table: 'user', name: 'id', type: 'serial', nullable: false)
+        ->primaryKey(table: 'user', ['id'])
+        ->column(table: 'user', name: 'enabled', type: 'bool', nullable: false, default: 'false')
+        ->column(table: 'user', 'email', 'text', true)
+        ->uniqueKey(table: 'user', columns: ['email'])
+        ->index(table: 'user', columns: ['email'])
+    ->commit()
+```
+
+:::note
+Table creation requires you to use the `createTable()` method nesting.
+:::
+
+### Conditions and branches
+
+You may write re-entrant schema alteration procedures by using conditional branches
+in the code, consider the previous example:
+
+```php
+$schemaManager
+    ->modify(database: 'my_database')
+        ->ifTableNotExists(table: 'user')
+            ->createTable(name: 'user')
+                ->column(name: 'id', type: 'serial', nullable: false)
+                ->primaryKey(['id'])
+                ->column(name: 'enabled', type: 'bool', nullable: false, default: 'false')
+            ->endTable()
+        ->endIf()
+        ->ifColumnNotExists(table: 'user', column: 'email')
+            ->column(table: 'user', 'email', 'text', true)
+            ->uniqueKey(table: 'user', columns: ['email'])
+            ->index(table: 'user', columns: ['email'])
+        ->endIf()
+    ->commit()
+```
+
+:::note
+There is no `else()` statement yet, it might be implemented in in the future.
+:::
+
+### Arbitrary SQL queries
+
+@todo
+
+### Using arbitrary SQL as condition
+
+@todo
+
+### Self-documenting example
+
 The `$transaction` object is an instance of `MakinaCorpus\QueryBuilder\Schema\Diff\SchemaTransaction`
 implementing the builder pattern, i.e. allowing method chaining.
 
diff --git a/src/Platform/Schema/MySQLSchemaManager.php b/src/Platform/Schema/MySQLSchemaManager.php
index 4e61a74..4444bdc 100644
--- a/src/Platform/Schema/MySQLSchemaManager.php
+++ b/src/Platform/Schema/MySQLSchemaManager.php
@@ -4,14 +4,10 @@
 
 namespace MakinaCorpus\QueryBuilder\Platform\Schema;
 
-use MakinaCorpus\QueryBuilder\Expression;
 use MakinaCorpus\QueryBuilder\Error\QueryBuilderError;
 use MakinaCorpus\QueryBuilder\Error\UnsupportedFeatureError;
+use MakinaCorpus\QueryBuilder\Expression;
 use MakinaCorpus\QueryBuilder\Result\ResultRow;
-use MakinaCorpus\QueryBuilder\Schema\Column;
-use MakinaCorpus\QueryBuilder\Schema\ForeignKey;
-use MakinaCorpus\QueryBuilder\Schema\Key;
-use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnModify;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ForeignKeyAdd;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\IndexCreate;
@@ -20,7 +16,10 @@
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\PrimaryKeyDrop;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyAdd;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyDrop;
-
+use MakinaCorpus\QueryBuilder\Schema\Read\Column;
+use MakinaCorpus\QueryBuilder\Schema\Read\ForeignKey;
+use MakinaCorpus\QueryBuilder\Schema\Read\Key;
+use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
 
 /**
  * Please note that some functions here might use information_schema tables
@@ -328,7 +327,7 @@ private function getAllTableKeysInfo(string $database, string $name, string $sch
     }
 
     #[\Override]
-    protected function writeColumnSpecCollation(string $collation): Expression
+    protected function doWriteColumnCollation(string $collation): Expression
     {
         // This is very hasardous, but let's do it.
         if ('binary' === $collation) {
@@ -348,16 +347,17 @@ protected function writeColumnSpecCollation(string $collation): Expression
     protected function writeColumnModify(ColumnModify $change): iterable|Expression
     {
         $name = $change->getName();
+        $type = $change->getType();
 
         // When modifying a column in MySQL, you need to use the CHANGE COLUMN
         // syntax if you change anything else than the DEFAULT value.
         // That's kind of very weird, but that's it. Live with it.
-        if ($change->getType() || null !== $change->isNullable() || $change->getCollation() || $change->getType()) {
+        if ($type || null !== $change->isNullable() || $change->getCollation()) {
             return $this->raw(
                 'ALTER TABLE ? MODIFY COLUMN ?',
                 [
                     $this->table($change),
-                    $this->writeColumnSpec($this->columnModifyToAdd($change)),
+                    $this->doWriteColumn($this->columnModifyToAdd($change)),
                 ]
             );
         }
@@ -371,20 +371,21 @@ protected function writeColumnModify(ColumnModify $change): iterable|Expression
             }
             $pieces[] = $this->raw('ALTER COLUMN ?::id DROP DEFAULT', [$name]);
         } else if ($default = $change->getDefault()) {
-            $pieces[] = $this->raw('ALTER COLUMN ?::id SET DEFAULT ?', [$name, $this->raw($default)]);
+            // @todo
+            $pieces[] = $this->raw('ALTER COLUMN ?::id SET DEFAULT ?', [$name, $this->doWriteColumnDefault($type ?? 'unknown', $default)]);
         }
 
         return $this->raw('ALTER TABLE ? ' . \implode(', ', \array_fill(0, \count($pieces), '?')), [$this->table($change), ...$pieces]);
     }
 
     #[\Override]
-    protected function writeForeignKeySpec(ForeignKeyAdd $change): Expression
+    protected function doWriteForeignKey(ForeignKeyAdd $change): Expression
     {
         if ($change->isDeferrable()) {
             // @todo log that MySQL doesn't support deferring?
         }
 
-        return $this->writeConstraintSpec(
+        return $this->doWriteConstraint(
             $change->getName(),
             $this->raw(
                 'FOREIGN KEY (?::id[]) REFERENCES ?::table (?::id[])',
@@ -440,6 +441,6 @@ protected function writeUniqueKeyAdd(UniqueKeyAdd $change): Expression
     #[\Override]
     protected function writeUniqueKeyDrop(UniqueKeyDrop $change): Expression
     {
-        return $this->writeConstraintDropSpec($change->getName(), $change->getTable(), $change->getSchema());
+        return $this->doWriteConstraintDrop($change->getName(), $change->getTable(), $change->getSchema());
     }
 }
diff --git a/src/Platform/Schema/PostgreSQLSchemaManager.php b/src/Platform/Schema/PostgreSQLSchemaManager.php
index b59f9e7..d5282d2 100644
--- a/src/Platform/Schema/PostgreSQLSchemaManager.php
+++ b/src/Platform/Schema/PostgreSQLSchemaManager.php
@@ -7,11 +7,11 @@
 use MakinaCorpus\QueryBuilder\Expression;
 use MakinaCorpus\QueryBuilder\Result\Result;
 use MakinaCorpus\QueryBuilder\Result\ResultRow;
-use MakinaCorpus\QueryBuilder\Schema\Column;
-use MakinaCorpus\QueryBuilder\Schema\ForeignKey;
-use MakinaCorpus\QueryBuilder\Schema\Key;
-use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\IndexRename;
+use MakinaCorpus\QueryBuilder\Schema\Read\Column;
+use MakinaCorpus\QueryBuilder\Schema\Read\ForeignKey;
+use MakinaCorpus\QueryBuilder\Schema\Read\Key;
+use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
 
 /**
  * Please note that some functions here might use information_schema tables
diff --git a/src/Platform/Schema/SQLiteSchemaManager.php b/src/Platform/Schema/SQLiteSchemaManager.php
index ca7bb42..eb6553e 100644
--- a/src/Platform/Schema/SQLiteSchemaManager.php
+++ b/src/Platform/Schema/SQLiteSchemaManager.php
@@ -4,13 +4,9 @@
 
 namespace MakinaCorpus\QueryBuilder\Platform\Schema;
 
-use MakinaCorpus\QueryBuilder\Expression;
 use MakinaCorpus\QueryBuilder\Error\UnsupportedFeatureError;
+use MakinaCorpus\QueryBuilder\Expression;
 use MakinaCorpus\QueryBuilder\Result\ResultRow;
-use MakinaCorpus\QueryBuilder\Schema\Column;
-use MakinaCorpus\QueryBuilder\Schema\ForeignKey;
-use MakinaCorpus\QueryBuilder\Schema\Key;
-use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnModify;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ConstraintDrop;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ConstraintModify;
@@ -24,6 +20,10 @@
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\PrimaryKeyAdd;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\PrimaryKeyDrop;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyAdd;
+use MakinaCorpus\QueryBuilder\Schema\Read\Column;
+use MakinaCorpus\QueryBuilder\Schema\Read\ForeignKey;
+use MakinaCorpus\QueryBuilder\Schema\Read\Key;
+use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
 
 /**
  * Please note that some functions here might use information_schema tables
diff --git a/src/Schema/Diff/Browser/ChangeLogBrowser.php b/src/Schema/Diff/Browser/ChangeLogBrowser.php
new file mode 100644
index 0000000..c1962bc
--- /dev/null
+++ b/src/Schema/Diff/Browser/ChangeLogBrowser.php
@@ -0,0 +1,110 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Browser;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\AbstractCondition;
+use MakinaCorpus\QueryBuilder\Schema\Diff\SchemaTransaction;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Transaction\AbstractNestedSchemaTransaction;
+
+class ChangeLogBrowser
+{
+    /** @var ChangeLogVisitor[] */
+    private array $visitors = [];
+
+    public function addVisitor(ChangeLogVisitor $visitor): void
+    {
+        $this->visitors[] = $visitor;
+    }
+
+    public function browse(SchemaTransaction $transaction): void
+    {
+        try {
+            foreach ($this->visitors as $visitor) {
+                $visitor->start($transaction);
+            }
+
+            foreach ($transaction->getChangeLog()->getAll() as $change) {
+                if ($change instanceof AbstractNestedSchemaTransaction) {
+                    $this->reduceNested($change, 1, $this->visitors);
+                } else {
+                    foreach ($this->visitors as $visitor) {
+                        $visitor->apply($change);
+                    }
+                }
+            }
+
+            foreach ($this->visitors as $visitor) {
+                $visitor->stop($transaction);
+            }
+        } catch (\Throwable $error) {
+            foreach ($this->visitors as $visitor) {
+                $visitor->error($transaction, $error);
+            }
+
+            throw $error;
+        }
+    }
+
+    /**
+     * @param AbstractCondition[] $conditions
+     */
+    protected function evaluateConditions(array $conditions, ChangeLogVisitor $visitor): bool
+    {
+        foreach ($conditions as $condition) {
+            if (!$visitor->evaluate($condition)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /**
+     * @param ChangeLogVisitor[] $visitors
+     */
+    protected function reduceNested(AbstractNestedSchemaTransaction $new, int $depth, array $visitors)
+    {
+        if ($conditions = $new->getConditions()) {
+            $candidates = [];
+
+            foreach ($visitors as $visitor) {
+                \assert($visitor instanceof ChangeLogVisitor);
+
+                if ($this->evaluateConditions($conditions, $visitor)) {
+                    $candidates[] = $visitor;
+                } else {
+                    $visitor->skip($new, $depth);
+                }
+            }
+
+            if ($candidates) {
+                $this->browseNested($new, $depth, $candidates);
+            }
+        }
+    }
+
+    /**
+     * @param ChangeLogVisitor[] $visitors
+     */
+    protected function browseNested(AbstractNestedSchemaTransaction $new, int $depth, array $visitors): void
+    {
+        foreach ($visitors as $visitor) {
+            $visitor->enter($new, $depth);
+        }
+
+        foreach ($new->getChangeLog()->getAll() as $change) {
+            if ($change instanceof AbstractNestedSchemaTransaction) {
+                $this->reduceNested($change, $depth + 1, $visitors);
+            } else {
+                foreach ($visitors as $visitor) {
+                    $visitor->apply($change);
+                }
+            }
+        }
+
+        foreach ($visitors as $visitor) {
+            $visitor->leave($new, $depth);
+        }
+    }
+}
diff --git a/src/Schema/Diff/Browser/ChangeLogVisitor.php b/src/Schema/Diff/Browser/ChangeLogVisitor.php
new file mode 100644
index 0000000..ba47379
--- /dev/null
+++ b/src/Schema/Diff/Browser/ChangeLogVisitor.php
@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Browser;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\AbstractChange;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\AbstractCondition;
+use MakinaCorpus\QueryBuilder\Schema\Diff\SchemaTransaction;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Transaction\AbstractNestedSchemaTransaction;
+
+abstract class ChangeLogVisitor
+{
+    /**
+     * Process starts.
+     */
+    public function start(SchemaTransaction $transaction): void
+    {
+    }
+
+    /**
+     * Process ends.
+     */
+    public function stop(SchemaTransaction $transaction): void
+    {
+    }
+
+    /**
+     * Process ends due to an error.
+     */
+    public function error(SchemaTransaction $transaction, \Throwable $error): void
+    {
+    }
+
+    /**
+     * Enter nesting level.
+     */
+    public function enter(AbstractNestedSchemaTransaction $nested, int $depth): void
+    {
+    }
+
+    /**
+     * Leave nesting level.
+     */
+    public function leave(AbstractNestedSchemaTransaction $nested, int $depth): void
+    {
+    }
+
+    /**
+     * Skip nesting level.
+     */
+    public function skip(AbstractNestedSchemaTransaction $nested, int $depth): void
+    {
+    }
+
+    /**
+     * Evaluate a single condition.
+     */
+    public function evaluate(AbstractCondition $condition): bool
+    {
+        return true;
+    }
+
+    /**
+     * Apply a single change.
+     */
+    public function apply(AbstractChange $change): void
+    {
+    }
+}
diff --git a/src/Schema/Diff/Browser/SchemaWriterDryRunLogVisitor.php b/src/Schema/Diff/Browser/SchemaWriterDryRunLogVisitor.php
new file mode 100644
index 0000000..8992e49
--- /dev/null
+++ b/src/Schema/Diff/Browser/SchemaWriterDryRunLogVisitor.php
@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Browser;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\AbstractChange;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\AbstractCondition;
+use MakinaCorpus\QueryBuilder\Schema\Diff\SchemaTransaction;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Transaction\AbstractNestedSchemaTransaction;
+
+class SchemaWriterDryRunLogVisitor extends ChangeLogVisitor
+{
+    /**
+     * Process starts.
+     */
+    public function start(SchemaTransaction $transaction): void
+    {
+    }
+
+    /**
+     * Process ends.
+     */
+    public function stop(SchemaTransaction $transaction): void
+    {
+    }
+
+    /**
+     * Process ends due to an error.
+     */
+    public function error(SchemaTransaction $transaction, \Throwable $error): void
+    {
+    }
+
+    /**
+     * Enter nesting level.
+     */
+    public function enter(AbstractNestedSchemaTransaction $nested, int $depth): void
+    {
+    }
+
+    /**
+     * Leave nesting level.
+     */
+    public function leave(AbstractNestedSchemaTransaction $nested, int $depth): void
+    {
+    }
+
+    /**
+     * Skip nesting level.
+     */
+    public function skip(AbstractNestedSchemaTransaction $nested, int $depth): void
+    {
+    }
+
+    /**
+     * Evaluate a single condition.
+     */
+    public function evaluate(AbstractCondition $condition): bool
+    {
+        return true;
+    }
+
+    /**
+     * Apply a single change.
+     */
+    public function apply(AbstractChange $change): void
+    {
+    }
+}
diff --git a/src/Schema/Diff/Browser/SchemaWriterLogVisitor.php b/src/Schema/Diff/Browser/SchemaWriterLogVisitor.php
new file mode 100644
index 0000000..1428ba0
--- /dev/null
+++ b/src/Schema/Diff/Browser/SchemaWriterLogVisitor.php
@@ -0,0 +1,89 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Browser;
+
+use MakinaCorpus\QueryBuilder\Error\QueryBuilderError;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\AbstractChange;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\AbstractCondition;
+use MakinaCorpus\QueryBuilder\Schema\Diff\SchemaTransaction;
+use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
+use MakinaCorpus\QueryBuilder\Transaction\Transaction;
+
+class SchemaWriterLogVisitor extends ChangeLogVisitor
+{
+    private ?Transaction $transaction = null;
+
+    public function __construct(
+        private SchemaManager $schema,
+    ) {}
+
+    private function dieIfNoTransaction(): void
+    {
+        if ($this->schema->supportsTransaction() && (!$this->transaction || !$this->transaction->isStarted())) {
+            throw new QueryBuilderError("Transaction should have been started here.");
+        }
+    }
+
+    private function dieIfTransaction(): void
+    {
+        if ($this->schema->supportsTransaction() && $this->transaction && !$this->transaction->isStarted()) {
+            throw new QueryBuilderError("Transaction should have not been started here.");
+        }
+    }
+
+    #[\Override]
+    public function start(SchemaTransaction $transaction): void
+    {
+        $this->dieIfTransaction();
+
+        if ($this->schema->supportsTransaction()) {
+            $this->transaction = $this->schema->getQueryExecutor()->beginTransaction(Transaction::SERIALIZABLE);
+        }
+    }
+
+    #[\Override]
+    public function stop(SchemaTransaction $transaction): void
+    {
+        $this->dieIfNoTransaction();
+
+        if ($this->schema->supportsTransaction()) {
+            try {
+                $this->transaction->commit();
+            } finally {
+                $this->transaction = null;
+            }
+        }
+    }
+
+    #[\Override]
+    public function error(SchemaTransaction $transaction, \Throwable $error): void
+    {
+        $this->dieIfNoTransaction();
+
+        if ($this->schema->supportsTransaction()) {
+            try {
+                $this->transaction->rollback();
+            } finally {
+                $this->transaction = null;
+            }
+        }
+    }
+
+    #[\Override]
+    public function evaluate(AbstractCondition $condition): bool
+    {
+        $this->dieIfNoTransaction();
+
+        return $this->schema->evaluateCondition($condition);
+    }
+
+    #[\Override]
+    public function apply(AbstractChange $change): void
+    {
+        $this->dieIfNoTransaction();
+
+        $this->schema->applyChange($change);
+    }
+}
diff --git a/src/Schema/Diff/AbstractChange.php b/src/Schema/Diff/Change/AbstractChange.php
similarity index 64%
rename from src/Schema/Diff/AbstractChange.php
rename to src/Schema/Diff/Change/AbstractChange.php
index 7d7335c..8e8ae6a 100644
--- a/src/Schema/Diff/AbstractChange.php
+++ b/src/Schema/Diff/Change/AbstractChange.php
@@ -2,23 +2,27 @@
 
 declare(strict_types=1);
 
-namespace MakinaCorpus\QueryBuilder\Schema\Diff;
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\ChangeLogItem;
 
 /**
  * Changes on the schema.
  */
-abstract class AbstractChange
+abstract class AbstractChange implements ChangeLogItem
 {
     public function __construct(
         private readonly string $database,
         private readonly string $schema,
     ) {}
 
+    #[\Override]
     public function getDatabase(): string
     {
         return $this->database;
     }
 
+    #[\Override]
     public function getSchema(): string
     {
         return $this->schema;
diff --git a/src/Schema/Diff/Change/ColumnAdd.php b/src/Schema/Diff/Change/ColumnAdd.php
index e2ac852..43dd793 100644
--- a/src/Schema/Diff/Change/ColumnAdd.php
+++ b/src/Schema/Diff/Change/ColumnAdd.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Add a COLUMN.
  *
diff --git a/src/Schema/Diff/Change/ColumnDrop.php b/src/Schema/Diff/Change/ColumnDrop.php
index 6a016fd..d61bea3 100644
--- a/src/Schema/Diff/Change/ColumnDrop.php
+++ b/src/Schema/Diff/Change/ColumnDrop.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Drop a COLUMN.
  *
diff --git a/src/Schema/Diff/Change/ColumnModify.php b/src/Schema/Diff/Change/ColumnModify.php
index 3436f3b..6437795 100644
--- a/src/Schema/Diff/Change/ColumnModify.php
+++ b/src/Schema/Diff/Change/ColumnModify.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Add a COLUMN.
  *
diff --git a/src/Schema/Diff/Change/ColumnRename.php b/src/Schema/Diff/Change/ColumnRename.php
index 06767c9..08e0635 100644
--- a/src/Schema/Diff/Change/ColumnRename.php
+++ b/src/Schema/Diff/Change/ColumnRename.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Renames a COLUMN.
  *
diff --git a/src/Schema/Diff/Change/ConstraintDrop.php b/src/Schema/Diff/Change/ConstraintDrop.php
index dd8346f..a668b0a 100644
--- a/src/Schema/Diff/Change/ConstraintDrop.php
+++ b/src/Schema/Diff/Change/ConstraintDrop.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Drop an arbitrary constraint from a table.
  *
diff --git a/src/Schema/Diff/Change/ConstraintModify.php b/src/Schema/Diff/Change/ConstraintModify.php
index 69b8705..24e69d8 100644
--- a/src/Schema/Diff/Change/ConstraintModify.php
+++ b/src/Schema/Diff/Change/ConstraintModify.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Modify an arbitrary constraint on a table.
  *
diff --git a/src/Schema/Diff/Change/ConstraintRename.php b/src/Schema/Diff/Change/ConstraintRename.php
index 24e511d..bc828f8 100644
--- a/src/Schema/Diff/Change/ConstraintRename.php
+++ b/src/Schema/Diff/Change/ConstraintRename.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Rename an arbitrary constraint.
  *
diff --git a/src/Schema/Diff/Change/ForeignKeyAdd.php b/src/Schema/Diff/Change/ForeignKeyAdd.php
index 94841cc..a940f4b 100644
--- a/src/Schema/Diff/Change/ForeignKeyAdd.php
+++ b/src/Schema/Diff/Change/ForeignKeyAdd.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Add a FOREIGN KEY constraint on a table.
  *
diff --git a/src/Schema/Diff/Change/ForeignKeyDrop.php b/src/Schema/Diff/Change/ForeignKeyDrop.php
index 1dba90e..3c75460 100644
--- a/src/Schema/Diff/Change/ForeignKeyDrop.php
+++ b/src/Schema/Diff/Change/ForeignKeyDrop.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Drop a FOREIGN KEY constraint from a table.
  *
diff --git a/src/Schema/Diff/Change/ForeignKeyModify.php b/src/Schema/Diff/Change/ForeignKeyModify.php
index 8e68a9b..88959d7 100644
--- a/src/Schema/Diff/Change/ForeignKeyModify.php
+++ b/src/Schema/Diff/Change/ForeignKeyModify.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Modify a FOREIGN KEY constraint on a table.
  *
diff --git a/src/Schema/Diff/Change/ForeignKeyRename.php b/src/Schema/Diff/Change/ForeignKeyRename.php
index b7b170a..80138cf 100644
--- a/src/Schema/Diff/Change/ForeignKeyRename.php
+++ b/src/Schema/Diff/Change/ForeignKeyRename.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Rename an arbitrary constraint.
  *
diff --git a/src/Schema/Diff/Change/IndexCreate.php b/src/Schema/Diff/Change/IndexCreate.php
index 105b7b8..7cc2946 100644
--- a/src/Schema/Diff/Change/IndexCreate.php
+++ b/src/Schema/Diff/Change/IndexCreate.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Create an INDEX on a table.
  *
diff --git a/src/Schema/Diff/Change/IndexDrop.php b/src/Schema/Diff/Change/IndexDrop.php
index a58905e..6021fa1 100644
--- a/src/Schema/Diff/Change/IndexDrop.php
+++ b/src/Schema/Diff/Change/IndexDrop.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Drop an INDEX from a table.
  *
diff --git a/src/Schema/Diff/Change/IndexRename.php b/src/Schema/Diff/Change/IndexRename.php
index 97182b5..83fe4a1 100644
--- a/src/Schema/Diff/Change/IndexRename.php
+++ b/src/Schema/Diff/Change/IndexRename.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Rename an arbitrary constraint.
  *
diff --git a/src/Schema/Diff/Change/PrimaryKeyAdd.php b/src/Schema/Diff/Change/PrimaryKeyAdd.php
index 79e5cec..af74484 100644
--- a/src/Schema/Diff/Change/PrimaryKeyAdd.php
+++ b/src/Schema/Diff/Change/PrimaryKeyAdd.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Add the PRIMARY KEY constraint on a table.
  *
diff --git a/src/Schema/Diff/Change/PrimaryKeyDrop.php b/src/Schema/Diff/Change/PrimaryKeyDrop.php
index 759b0e0..97b98ba 100644
--- a/src/Schema/Diff/Change/PrimaryKeyDrop.php
+++ b/src/Schema/Diff/Change/PrimaryKeyDrop.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Drop the PRIMARY KEY constraint from a table.
  *
diff --git a/src/Schema/Diff/Change/TableCreate.php b/src/Schema/Diff/Change/TableCreate.php
index aa40bda..9ee36e3 100644
--- a/src/Schema/Diff/Change/TableCreate.php
+++ b/src/Schema/Diff/Change/TableCreate.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Create a table.
  *
diff --git a/src/Schema/Diff/Change/TableDrop.php b/src/Schema/Diff/Change/TableDrop.php
index ca4ebf6..726a99f 100644
--- a/src/Schema/Diff/Change/TableDrop.php
+++ b/src/Schema/Diff/Change/TableDrop.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Drop a table.
  *
diff --git a/src/Schema/Diff/Change/TableRename.php b/src/Schema/Diff/Change/TableRename.php
index 7486a2c..b931249 100644
--- a/src/Schema/Diff/Change/TableRename.php
+++ b/src/Schema/Diff/Change/TableRename.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Renames a table.
  *
diff --git a/src/Schema/Diff/Change/UniqueKeyAdd.php b/src/Schema/Diff/Change/UniqueKeyAdd.php
index 2451e80..3aa7a5e 100644
--- a/src/Schema/Diff/Change/UniqueKeyAdd.php
+++ b/src/Schema/Diff/Change/UniqueKeyAdd.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Create a UNIQUE constraint on a table.
  *
diff --git a/src/Schema/Diff/Change/UniqueKeyDrop.php b/src/Schema/Diff/Change/UniqueKeyDrop.php
index baee084..07a68ad 100644
--- a/src/Schema/Diff/Change/UniqueKeyDrop.php
+++ b/src/Schema/Diff/Change/UniqueKeyDrop.php
@@ -4,8 +4,6 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-
 /**
  * Drop a UNIQUE constraint from a table.
  *
diff --git a/src/Schema/Diff/ChangeLog.php b/src/Schema/Diff/ChangeLog.php
index 92082e8..7ed1e5d 100644
--- a/src/Schema/Diff/ChangeLog.php
+++ b/src/Schema/Diff/ChangeLog.php
@@ -4,34 +4,23 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff;
 
-use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
-
 class ChangeLog
 {
     public function __construct(
-        private readonly SchemaManager $schemaManager,
-        /** @var AbstractChange[] */
+        /** @var ChangeLogItem[] */
         private array $changes = [],
     ) {}
 
-    public function add(AbstractChange $change): void
+    public function add(ChangeLogItem $change): void
     {
         $this->changes[] = $change;
     }
 
+    /**
+     * @return ChangeLogItem[]
+     */
     public function getAll(): iterable
     {
         return $this->changes;
     }
-
-    public function diff(): ChangeLog
-    {
-        foreach ($this->changes as $change) {
-            // load target object
-            // run has modified
-        }
-
-        // @todo fix this
-        return $this;
-    }
 }
diff --git a/src/Schema/Diff/ChangeLogItem.php b/src/Schema/Diff/ChangeLogItem.php
new file mode 100644
index 0000000..35e80e1
--- /dev/null
+++ b/src/Schema/Diff/ChangeLogItem.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff;
+
+interface ChangeLogItem
+{
+    /**
+     * Get database this change acts upon.
+     */
+    public function getDatabase(): string;
+
+    /**
+     * Get schema this change acts upon.
+     */
+    public function getSchema(): string;
+}
diff --git a/src/Schema/Diff/Condition/AbstractCondition.php b/src/Schema/Diff/Condition/AbstractCondition.php
new file mode 100644
index 0000000..58e0c6c
--- /dev/null
+++ b/src/Schema/Diff/Condition/AbstractCondition.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Condition;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\ChangeLogItem;
+
+/**
+ * Condition on the schema that returns true or false.
+ */
+abstract class AbstractCondition implements ChangeLogItem
+{
+    public function __construct(
+        private readonly string $database,
+        private readonly string $schema,
+        private readonly bool $negation = false,
+    ) {}
+
+    #[\Override]
+    public function getDatabase(): string
+    {
+        return $this->database;
+    }
+
+    #[\Override]
+    public function getSchema(): string
+    {
+        return $this->schema;
+    }
+
+    public function isNegation(): bool
+    {
+        return $this->negation;
+    }
+}
diff --git a/src/Schema/Diff/Condition/ColumnExists.php b/src/Schema/Diff/Condition/ColumnExists.php
new file mode 100644
index 0000000..1078882
--- /dev/null
+++ b/src/Schema/Diff/Condition/ColumnExists.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Condition;
+
+class ColumnExists extends AbstractCondition
+{
+    public function __construct(
+        string $database,
+        string $schema,
+        private readonly string $table,
+        private readonly string $column,
+        bool $negation = false,
+    ) {
+        parent::__construct($database, $schema, $negation);
+    }
+
+    public function getTable(): string
+    {
+        return $this->table;
+    }
+
+    public function getColumn(): string
+    {
+        return $this->column;
+    }
+}
diff --git a/src/Schema/Diff/Condition/IndexExists.php b/src/Schema/Diff/Condition/IndexExists.php
new file mode 100644
index 0000000..3e4e685
--- /dev/null
+++ b/src/Schema/Diff/Condition/IndexExists.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Condition;
+
+class IndexExists extends AbstractCondition
+{
+    public function __construct(
+        string $database,
+        string $schema,
+        private readonly string $table,
+        /** @var string[] */
+        private readonly array $columns,
+        bool $negation = false,
+    ) {
+        parent::__construct($database, $schema, $negation);
+    }
+
+    public function getTable(): string
+    {
+        return $this->table;
+    }
+
+    /** @return string[] */
+    public function getColumns(): array
+    {
+        return $this->columns;
+    }
+}
diff --git a/src/Schema/Diff/Condition/TableExists.php b/src/Schema/Diff/Condition/TableExists.php
new file mode 100644
index 0000000..e576b82
--- /dev/null
+++ b/src/Schema/Diff/Condition/TableExists.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Condition;
+
+class TableExists extends AbstractCondition
+{
+    public function __construct(
+        string $database,
+        string $schema,
+        private readonly string $table,
+        bool $negation = false,
+    ) {
+        parent::__construct($database, $schema, $negation);
+    }
+
+    public function getTable(): string
+    {
+        return $this->table;
+    }
+}
diff --git a/src/Schema/Diff/Change/Template/Generator.php b/src/Schema/Diff/Generator/Generator.php
similarity index 94%
rename from src/Schema/Diff/Change/Template/Generator.php
rename to src/Schema/Diff/Generator/Generator.php
index 58119d9..395faf7 100644
--- a/src/Schema/Diff/Change/Template/Generator.php
+++ b/src/Schema/Diff/Generator/Generator.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace MakinaCorpus\QueryBuilder\Schema\Diff\Change\Template;
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Generator;
 
 use MakinaCorpus\QueryBuilder\Error\QueryBuilderError;
 
@@ -260,16 +260,15 @@ public function generateFromFile(): void
         $transactionMethodsString = \implode("\n\n", $additional['transaction']['methods']);
         $transactionUse = \implode("\n", $additional['transaction']['use']);
 
-        $schemaTransaction = <<<EOT
+        $changeLogBuilder = <<<EOT
             <?php
             
             declare(strict_types=1);
             
-            namespace MakinaCorpus\QueryBuilder\Schema\Diff;
+            namespace MakinaCorpus\QueryBuilder\Schema\Diff\Transaction;
             
+            use MakinaCorpus\QueryBuilder\Schema\Diff\ChangeLogItem;
             {$transactionUse}
-            use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-            use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
             
             /**
              * This code is generated using bin/generate_changes.php.
@@ -279,33 +278,12 @@ public function generateFromFile(): void
              * @see \\MakinaCorpus\\QueryBuilder\\Schema\\Diff\\Change\\Template\\Generator
              * @see bin/generate_changes.php
              */
-            class SchemaTransaction
+            abstract class GeneratedAbstractTransaction
             {
-                private ChangeLog \$changeLog;
-            
                 public function __construct(
-                    private readonly SchemaManager \$schemaManager,
-                    private readonly string \$database,
-                    private readonly string \$schema,
-                    private readonly \Closure \$onCommit,
-                ) {
-                    \$this->changeLog = new ChangeLog(\$schemaManager);
-                }
-                
-                public function commit(): void
-                {
-                    (\$this->onCommit)(\$this->changeLog->diff());
-                }
-            
-            {$transactionMethodsString}
-            
-                /**
-                 * Create a table builder.
-                 */
-                public function createTable(string \$name): TableBuilder
-                {
-                    return new TableBuilder(parent: \$this, database: \$this->database, name: \$name, schema: \$this->schema);
-                }
+                    protected readonly string \$database,
+                    protected readonly string \$schema,
+                ) {}
             
                 /**
                  * Add new arbitrary change.
@@ -313,14 +291,13 @@ public function createTable(string \$name): TableBuilder
                  * @internal
                  *   For builders use only.
                  */
-                public function logChange(AbstractChange \$change): void
-                {
-                    \$this->changeLog->add(\$change);
-                }
+                public abstract function logChange(ChangeLogItem \$change): void;
+            
+            {$transactionMethodsString}
             }
             EOT;
 
-        \file_put_contents(\dirname(__DIR__, 2) . '/SchemaTransaction.php', $schemaTransaction . "\n");
+        \file_put_contents(\dirname(__DIR__) . '/Transaction/GeneratedAbstractTransaction.php', $changeLogBuilder . "\n");
     }
 
     private function camelize(string $input, bool $first = true): string
@@ -591,8 +568,6 @@ public function generateName(): string
         
         namespace MakinaCorpus\\QueryBuilder\\Schema\\Diff\\Change;
         
-        use MakinaCorpus\\QueryBuilder\\Schema\\Diff\\AbstractChange;
-        
         {$description}
         class {$className} extends AbstractChange
         {{$classConstantsString}
@@ -610,7 +585,7 @@ public function __construct(
         }
         EOT;
 
-        \file_put_contents(\dirname(__DIR__) . '/' . $className . '.php', $file . "\n");
+        \file_put_contents(\dirname(__DIR__) . '/Change/' . $className . '.php', $file . "\n");
 
         /*
          * Transaction methods and code.
@@ -640,7 +615,7 @@ public function {$transactionMethodName}(
                         {$transactionPropertiesString}
                         ?string \$schema = null,
                     ): static {
-                        \$this->changeLog->add(
+                        \$this->logChange(
                             new {$className}(
                                 {$transactionParametersString}
                                 schema: \$schema ?? \$this->schema,
diff --git a/src/Schema/Diff/SchemaTransaction.php b/src/Schema/Diff/SchemaTransaction.php
index ef317cb..0143602 100644
--- a/src/Schema/Diff/SchemaTransaction.php
+++ b/src/Schema/Diff/SchemaTransaction.php
@@ -4,537 +4,83 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema\Diff;
 
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnAdd;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnModify;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnDrop;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnRename;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ConstraintDrop;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ConstraintModify;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ConstraintRename;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ForeignKeyAdd;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ForeignKeyModify;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ForeignKeyDrop;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ForeignKeyRename;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\IndexCreate;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\IndexDrop;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\IndexRename;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\PrimaryKeyAdd;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\PrimaryKeyDrop;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\TableDrop;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\TableRename;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyAdd;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyDrop;
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
-
-/**
- * This code is generated using bin/generate_changes.php.
- *
- * Please do not modify it manually.
- *
- * @see \MakinaCorpus\QueryBuilder\Schema\Diff\Change\Template\Generator
- * @see bin/generate_changes.php
- */
-class SchemaTransaction
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\ColumnExists;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\IndexExists;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\TableExists;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Transaction\AbstractSchemaTransaction;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Transaction\NestedSchemaTransaction;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Transaction\TableBuilder;
+
+class SchemaTransaction extends AbstractSchemaTransaction
 {
     private ChangeLog $changeLog;
 
     public function __construct(
-        private readonly SchemaManager $schemaManager,
-        private readonly string $database,
-        private readonly string $schema,
+        string $database,
+        string $schema,
         private readonly \Closure $onCommit,
     ) {
-        $this->changeLog = new ChangeLog($schemaManager);
+        parent::__construct($database, $schema);
     }
-    
+
     public function commit(): void
     {
-        ($this->onCommit)($this->changeLog->diff());
-    }
-
-    /**
-     * Add a COLUMN.
-     */
-    public function addColumn(
-        string $table,
-        string $name,
-        string $type,
-        bool $nullable,
-        null|string $default = null,
-        null|string $collation = null,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ColumnAdd(
-                table: $table,
-                name: $name,
-                type: $type,
-                nullable: $nullable,
-                default: $default,
-                collation: $collation,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Add a COLUMN.
-     */
-    public function modifyColumn(
-        string $table,
-        string $name,
-        null|string $type = null,
-        null|bool $nullable = null,
-        null|string $default = null,
-        bool $dropDefault = false,
-        null|string $collation = null,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ColumnModify(
-                table: $table,
-                name: $name,
-                type: $type,
-                nullable: $nullable,
-                default: $default,
-                dropDefault: $dropDefault,
-                collation: $collation,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Drop a COLUMN.
-     */
-    public function dropColumn(
-        string $table,
-        string $name,
-        bool $cascade = false,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ColumnDrop(
-                table: $table,
-                name: $name,
-                cascade: $cascade,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Renames a COLUMN.
-     */
-    public function renameColumn(
-        string $table,
-        string $name,
-        string $newName,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ColumnRename(
-                table: $table,
-                name: $name,
-                newName: $newName,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Drop an arbitrary constraint from a table.
-     */
-    public function dropConstraint(
-        string $table,
-        string $name,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ConstraintDrop(
-                table: $table,
-                name: $name,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Modify an arbitrary constraint on a table.
-     */
-    public function modifyConstraint(
-        string $table,
-        string $name,
-        bool $deferrable = true,
-        string $initially = ConstraintModify::INITIALLY_DEFERRED,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ConstraintModify(
-                table: $table,
-                name: $name,
-                deferrable: $deferrable,
-                initially: $initially,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Rename an arbitrary constraint.
-     */
-    public function renameConstraint(
-        string $table,
-        string $name,
-        string $newName,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ConstraintRename(
-                table: $table,
-                name: $name,
-                newName: $newName,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Add a FOREIGN KEY constraint on a table.
-     */
-    public function addForeignKey(
-        string $table,
-        array $columns,
-        string $foreignTable,
-        array $foreignColumns,
-        null|string $name = null,
-        null|string $foreignSchema = null,
-        string $onDelete = ForeignKeyAdd::ON_DELETE_NO_ACTION,
-        string $onUpdate = ForeignKeyAdd::ON_UPDATE_NO_ACTION,
-        bool $deferrable = true,
-        string $initially = ForeignKeyAdd::INITIALLY_DEFERRED,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ForeignKeyAdd(
-                table: $table,
-                name: $name,
-                columns: $columns,
-                foreignTable: $foreignTable,
-                foreignColumns: $foreignColumns,
-                foreignSchema: $foreignSchema,
-                onDelete: $onDelete,
-                onUpdate: $onUpdate,
-                deferrable: $deferrable,
-                initially: $initially,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Modify a FOREIGN KEY constraint on a table.
-     */
-    public function modifyForeignKey(
-        string $table,
-        string $name,
-        string $onDelete = ForeignKeyModify::ON_DELETE_NO_ACTION,
-        string $onUpdate = ForeignKeyModify::ON_UPDATE_NO_ACTION,
-        bool $deferrable = true,
-        string $initially = ForeignKeyModify::INITIALLY_DEFERRED,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ForeignKeyModify(
-                table: $table,
-                name: $name,
-                onDelete: $onDelete,
-                onUpdate: $onUpdate,
-                deferrable: $deferrable,
-                initially: $initially,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
+        ($this->onCommit)($this);
     }
 
     /**
-     * Drop a FOREIGN KEY constraint from a table.
-     */
-    public function dropForeignKey(
-        string $table,
-        string $name,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ForeignKeyDrop(
-                table: $table,
-                name: $name,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Rename an arbitrary constraint.
-     */
-    public function renameForeignKey(
-        string $table,
-        string $name,
-        string $newName,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new ForeignKeyRename(
-                table: $table,
-                name: $name,
-                newName: $newName,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Create an INDEX on a table.
-     */
-    public function createIndex(
-        string $table,
-        array $columns,
-        null|string $name = null,
-        null|string $type = null,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new IndexCreate(
-                table: $table,
-                name: $name,
-                columns: $columns,
-                type: $type,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Drop an INDEX from a table.
-     */
-    public function dropIndex(
-        string $table,
-        string $name,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new IndexDrop(
-                table: $table,
-                name: $name,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Rename an arbitrary constraint.
-     */
-    public function renameIndex(
-        string $table,
-        string $name,
-        string $newName,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new IndexRename(
-                table: $table,
-                name: $name,
-                newName: $newName,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Add the PRIMARY KEY constraint on a table.
-     */
-    public function addPrimaryKey(
-        string $table,
-        array $columns,
-        null|string $name = null,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new PrimaryKeyAdd(
-                table: $table,
-                name: $name,
-                columns: $columns,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
-    }
-
-    /**
-     * Drop the PRIMARY KEY constraint from a table.
+     * Create a table builder.
      */
-    public function dropPrimaryKey(
-        string $table,
-        string $name,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new PrimaryKeyDrop(
-                table: $table,
-                name: $name,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
+    public function createTable(string $name): TableBuilder
+    {
+        return new TableBuilder(parent: $this, database: $this->database, name: $name, schema: $this->schema);
     }
 
     /**
-     * Drop a table.
+     * If table exists then.
      */
-    public function dropTable(
-        string $name,
-        bool $cascade = false,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new TableDrop(
-                name: $name,
-                cascade: $cascade,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
+    public function ifTableExists(string $table): NestedSchemaTransaction
+    {
+        return $this->nestWithCondition(new TableExists($this->database, $this->schema, $table));
     }
 
     /**
-     * Renames a table.
+     * If table does not exist then.
      */
-    public function renameTable(
-        string $name,
-        string $newName,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new TableRename(
-                name: $name,
-                newName: $newName,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
+    public function ifTableNotExists(string $table): NestedSchemaTransaction
+    {
+        return $this->nestWithCondition(new TableExists($this->database, $this->schema, $table, true));
     }
 
     /**
-     * Create a UNIQUE constraint on a table.
+     * If column exists then.
      */
-    public function addUniqueKey(
-        string $table,
-        array $columns,
-        null|string $name = null,
-        bool $nullsDistinct = true,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new UniqueKeyAdd(
-                table: $table,
-                name: $name,
-                columns: $columns,
-                nullsDistinct: $nullsDistinct,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
+    public function ifColumnExists(string $table, string $column): NestedSchemaTransaction
+    {
+        return $this->nestWithCondition(new ColumnExists($this->database, $this->schema, $table, $column));
     }
 
     /**
-     * Drop a UNIQUE constraint from a table.
+     * If column does not exist then.
      */
-    public function dropUniqueKey(
-        string $table,
-        string $name,
-        ?string $schema = null,
-    ): static {
-        $this->changeLog->add(
-            new UniqueKeyDrop(
-                table: $table,
-                name: $name,
-                schema: $schema ?? $this->schema,
-                database: $this->database,
-            )
-        );
-
-        return $this;
+    public function ifColumnNotExists(string $table, string $column): NestedSchemaTransaction
+    {
+        return $this->nestWithCondition(new ColumnExists($this->database, $this->schema, $table, $column, true));
     }
 
     /**
-     * Create a table builder.
+     * If index exists then.
      */
-    public function createTable(string $name): TableBuilder
+    public function ifIndexExists(string $table, array $columns): NestedSchemaTransaction
     {
-        return new TableBuilder(parent: $this, database: $this->database, name: $name, schema: $this->schema);
+        return $this->nestWithCondition(new IndexExists($this->database, $this->schema, $table, $columns));
     }
 
     /**
-     * Add new arbitrary change.
-     *
-     * @internal
-     *   For builders use only.
+     * If index does not exist then.
      */
-    public function logChange(AbstractChange $change): void
+    public function ifIndexNotExists(string $table, array $columns): NestedSchemaTransaction
     {
-        $this->changeLog->add($change);
+        return $this->nestWithCondition(new IndexExists($this->database, $this->schema, $table, $columns, true));
     }
 }
diff --git a/src/Schema/Diff/Transaction/AbstractNestedSchemaTransaction.php b/src/Schema/Diff/Transaction/AbstractNestedSchemaTransaction.php
new file mode 100644
index 0000000..601c1e5
--- /dev/null
+++ b/src/Schema/Diff/Transaction/AbstractNestedSchemaTransaction.php
@@ -0,0 +1,93 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Transaction;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\ChangeLogItem;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\ColumnExists;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\IndexExists;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\TableExists;
+
+/**
+ * @internal
+ *   Exists because PHP has no genericity.
+ */
+abstract class AbstractNestedSchemaTransaction extends AbstractSchemaTransaction implements ChangeLogItem
+{
+    public function __construct(
+        string $database,
+        string $schema,
+        private readonly array $conditions = [],
+    ) {
+        parent::__construct($database, $schema);
+    }
+
+    #[\Override]
+    public function getDatabase(): string
+    {
+        return $this->database;
+    }
+
+    #[\Override]
+    public function getSchema(): string
+    {
+        return $this->schema;
+    }
+
+    /**
+     * If table exists then.
+     */
+    public function ifTableExists(string $table): DeepNestedSchemaTransaction
+    {
+        return $this->nestWithCondition(new TableExists($this->database, $this->schema, $table));
+    }
+
+    /**
+     * If table does not exist then.
+     */
+    public function ifTableNotExists(string $table): DeepNestedSchemaTransaction
+    {
+        return $this->nestWithCondition(new TableExists($this->database, $this->schema, $table, true));
+    }
+
+    /**
+     * If column exists then.
+     */
+    public function ifColumnExists(string $table, string $column): DeepNestedSchemaTransaction
+    {
+        return $this->nestWithCondition(new ColumnExists($this->database, $this->schema, $table, $column));
+    }
+
+    /**
+     * If column does not exist then.
+     */
+    public function ifColumnNotExists(string $table, string $column): DeepNestedSchemaTransaction
+    {
+        return $this->nestWithCondition(new ColumnExists($this->database, $this->schema, $table, $column, true));
+    }
+
+    /**
+     * If index exists then.
+     */
+    public function ifIndexExists(string $table, array $columns): DeepNestedSchemaTransaction
+    {
+        return $this->nestWithCondition(new IndexExists($this->database, $this->schema, $table, $columns));
+    }
+
+    /**
+     * If index does not exist then.
+     */
+    public function ifIndexNotExists(string $table, array $columns): DeepNestedSchemaTransaction
+    {
+        return $this->nestWithCondition(new IndexExists($this->database, $this->schema, $table, $columns, true));
+    }
+
+    /**
+     * Get all conditions. No conditions means always execute.
+     */
+    public function getConditions(): array
+    {
+        return $this->conditions;
+    }
+}
diff --git a/src/Schema/Diff/Transaction/AbstractSchemaTransaction.php b/src/Schema/Diff/Transaction/AbstractSchemaTransaction.php
new file mode 100644
index 0000000..5ba8316
--- /dev/null
+++ b/src/Schema/Diff/Transaction/AbstractSchemaTransaction.php
@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Transaction;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\ChangeLog;
+use MakinaCorpus\QueryBuilder\Schema\Diff\ChangeLogItem;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\AbstractCondition;
+
+/**
+ * @internal
+ *   Exists because PHP has no genericity.
+ */
+abstract class AbstractSchemaTransaction extends GeneratedAbstractTransaction
+{
+    private ChangeLog $changeLog;
+
+    public function __construct(
+        string $database,
+        string $schema,
+    ) {
+        parent::__construct($database, $schema);
+
+        $this->changeLog = new ChangeLog();
+    }
+
+    /**
+     * Get current change log.
+     */
+    public function getChangeLog(): ChangeLog
+    {
+        return $this->changeLog;
+    }
+
+    /**
+     * Create nested instance with given conditions.
+     */
+    protected function nestWithCondition(AbstractCondition ...$conditions): NestedSchemaTransaction|DeepNestedSchemaTransaction
+    {
+        if ($this instanceof NestedSchemaTransaction || $this instanceof DeepNestedSchemaTransaction) {
+            $ret = new DeepNestedSchemaTransaction($this, $this->database, $this->schema, $conditions);
+        } else {
+            $ret = new NestedSchemaTransaction($this, $this->database, $this->schema, $conditions);
+        }
+
+        $this->logChange($ret);
+
+        return $ret;
+    }
+
+    #[\Override]
+    public function logChange(ChangeLogItem $change): void
+    {
+        $this->changeLog->add($change);
+    }
+}
diff --git a/src/Schema/Diff/TableBuilder.php b/src/Schema/Diff/Transaction/AbstractTableBuilder.php
similarity index 94%
rename from src/Schema/Diff/TableBuilder.php
rename to src/Schema/Diff/Transaction/AbstractTableBuilder.php
index 5e0198b..3ece8ee 100644
--- a/src/Schema/Diff/TableBuilder.php
+++ b/src/Schema/Diff/Transaction/AbstractTableBuilder.php
@@ -2,19 +2,20 @@
 
 declare(strict_types=1);
 
-namespace MakinaCorpus\QueryBuilder\Schema\Diff;
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Transaction;
 
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnAdd;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ForeignKeyAdd;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\IndexCreate;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\PrimaryKeyAdd;
-use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyAdd;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\TableCreate;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyAdd;
 
 /**
- * Table builder, for chaining calls with schema transaction.
+ * @internal
+ *   Exists because PHP has no genericity.
  */
-class TableBuilder
+abstract class AbstractTableBuilder
 {
     /** @var ColumnAdd[] */
     private array $columns = [];
@@ -28,7 +29,7 @@ class TableBuilder
     private bool $temporary = false;
 
     public function __construct(
-        private readonly SchemaTransaction $parent,
+        private readonly GeneratedAbstractTransaction $parent,
         private readonly string $database,
         private readonly string $name,
         private string $schema,
@@ -162,9 +163,9 @@ public function index(array $columns, ?string $name = null, ?string $type = null
     }
 
     /**
-     * Table is done.
+     * Create and log table.
      */
-    public function endTable(): SchemaTransaction
+    protected function createAndLogTable(): void
     {
         $this->parent->logChange(
             new TableCreate(
@@ -179,7 +180,5 @@ public function endTable(): SchemaTransaction
                 uniqueKeys: $this->uniqueKeys,
             ),
         );
-
-        return $this->parent;
     }
 }
diff --git a/src/Schema/Diff/Transaction/DeepNestedSchemaTransaction.php b/src/Schema/Diff/Transaction/DeepNestedSchemaTransaction.php
new file mode 100644
index 0000000..a2a2bec
--- /dev/null
+++ b/src/Schema/Diff/Transaction/DeepNestedSchemaTransaction.php
@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Transaction;
+
+/**
+ * @internal
+ *   Exists because PHP has no genericity.
+ */
+class DeepNestedSchemaTransaction extends AbstractNestedSchemaTransaction
+{
+    public function __construct(
+        private readonly NestedSchemaTransaction $parent,
+        string $database,
+        string $schema,
+        array $conditions = [],
+    ) {
+        parent::__construct($database, $schema, $conditions);
+    }
+
+    /**
+     * Create a table builder.
+     */
+    public function createTable(string $name): DeepNestedTableBuilder
+    {
+        return new DeepNestedTableBuilder(parent: $this, database: $this->database, name: $name, schema: $this->schema);
+    }
+
+    /**
+     * End nested branch and go back to parent.
+     */
+    public function endIf(): NestedSchemaTransaction
+    {
+        return $this->parent;
+    }
+}
diff --git a/src/Schema/Diff/Transaction/DeepNestedTableBuilder.php b/src/Schema/Diff/Transaction/DeepNestedTableBuilder.php
new file mode 100644
index 0000000..5ab61e9
--- /dev/null
+++ b/src/Schema/Diff/Transaction/DeepNestedTableBuilder.php
@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Transaction;
+
+/**
+ * @internal
+ *   Exists because PHP has no genericity.
+ */
+class DeepNestedTableBuilder extends AbstractTableBuilder
+{
+    public function __construct(
+        private readonly DeepNestedSchemaTransaction $parent,
+        string $database,
+        string $name,
+        string $schema,
+    ) {
+        parent::__construct($parent, $database, $name, $schema);
+    }
+
+    /**
+     * Table is done.
+     */
+    public function endTable(): DeepNestedSchemaTransaction
+    {
+        $this->createAndLogTable();
+
+        return $this->parent;
+    }
+}
diff --git a/src/Schema/Diff/Transaction/GeneratedAbstractTransaction.php b/src/Schema/Diff/Transaction/GeneratedAbstractTransaction.php
new file mode 100644
index 0000000..53ca612
--- /dev/null
+++ b/src/Schema/Diff/Transaction/GeneratedAbstractTransaction.php
@@ -0,0 +1,517 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Transaction;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\ChangeLogItem;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnAdd;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnModify;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnDrop;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnRename;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ConstraintDrop;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ConstraintModify;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ConstraintRename;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ForeignKeyAdd;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ForeignKeyModify;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ForeignKeyDrop;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ForeignKeyRename;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\IndexCreate;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\IndexDrop;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\IndexRename;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\PrimaryKeyAdd;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\PrimaryKeyDrop;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\TableDrop;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\TableRename;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyAdd;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyDrop;
+
+/**
+ * This code is generated using bin/generate_changes.php.
+ *
+ * Please do not modify it manually.
+ *
+ * @see \MakinaCorpus\QueryBuilder\Schema\Diff\Change\Template\Generator
+ * @see bin/generate_changes.php
+ */
+abstract class GeneratedAbstractTransaction
+{
+    public function __construct(
+        protected readonly string $database,
+        protected readonly string $schema,
+    ) {}
+
+    /**
+     * Add new arbitrary change.
+     *
+     * @internal
+     *   For builders use only.
+     */
+    public abstract function logChange(ChangeLogItem $change): void;
+
+    /**
+     * Add a COLUMN.
+     */
+    public function addColumn(
+        string $table,
+        string $name,
+        string $type,
+        bool $nullable,
+        null|string $default = null,
+        null|string $collation = null,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ColumnAdd(
+                table: $table,
+                name: $name,
+                type: $type,
+                nullable: $nullable,
+                default: $default,
+                collation: $collation,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Add a COLUMN.
+     */
+    public function modifyColumn(
+        string $table,
+        string $name,
+        null|string $type = null,
+        null|bool $nullable = null,
+        null|string $default = null,
+        bool $dropDefault = false,
+        null|string $collation = null,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ColumnModify(
+                table: $table,
+                name: $name,
+                type: $type,
+                nullable: $nullable,
+                default: $default,
+                dropDefault: $dropDefault,
+                collation: $collation,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Drop a COLUMN.
+     */
+    public function dropColumn(
+        string $table,
+        string $name,
+        bool $cascade = false,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ColumnDrop(
+                table: $table,
+                name: $name,
+                cascade: $cascade,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Renames a COLUMN.
+     */
+    public function renameColumn(
+        string $table,
+        string $name,
+        string $newName,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ColumnRename(
+                table: $table,
+                name: $name,
+                newName: $newName,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Drop an arbitrary constraint from a table.
+     */
+    public function dropConstraint(
+        string $table,
+        string $name,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ConstraintDrop(
+                table: $table,
+                name: $name,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Modify an arbitrary constraint on a table.
+     */
+    public function modifyConstraint(
+        string $table,
+        string $name,
+        bool $deferrable = true,
+        string $initially = ConstraintModify::INITIALLY_DEFERRED,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ConstraintModify(
+                table: $table,
+                name: $name,
+                deferrable: $deferrable,
+                initially: $initially,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Rename an arbitrary constraint.
+     */
+    public function renameConstraint(
+        string $table,
+        string $name,
+        string $newName,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ConstraintRename(
+                table: $table,
+                name: $name,
+                newName: $newName,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Add a FOREIGN KEY constraint on a table.
+     */
+    public function addForeignKey(
+        string $table,
+        array $columns,
+        string $foreignTable,
+        array $foreignColumns,
+        null|string $name = null,
+        null|string $foreignSchema = null,
+        string $onDelete = ForeignKeyAdd::ON_DELETE_NO_ACTION,
+        string $onUpdate = ForeignKeyAdd::ON_UPDATE_NO_ACTION,
+        bool $deferrable = true,
+        string $initially = ForeignKeyAdd::INITIALLY_DEFERRED,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ForeignKeyAdd(
+                table: $table,
+                name: $name,
+                columns: $columns,
+                foreignTable: $foreignTable,
+                foreignColumns: $foreignColumns,
+                foreignSchema: $foreignSchema,
+                onDelete: $onDelete,
+                onUpdate: $onUpdate,
+                deferrable: $deferrable,
+                initially: $initially,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Modify a FOREIGN KEY constraint on a table.
+     */
+    public function modifyForeignKey(
+        string $table,
+        string $name,
+        string $onDelete = ForeignKeyModify::ON_DELETE_NO_ACTION,
+        string $onUpdate = ForeignKeyModify::ON_UPDATE_NO_ACTION,
+        bool $deferrable = true,
+        string $initially = ForeignKeyModify::INITIALLY_DEFERRED,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ForeignKeyModify(
+                table: $table,
+                name: $name,
+                onDelete: $onDelete,
+                onUpdate: $onUpdate,
+                deferrable: $deferrable,
+                initially: $initially,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Drop a FOREIGN KEY constraint from a table.
+     */
+    public function dropForeignKey(
+        string $table,
+        string $name,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ForeignKeyDrop(
+                table: $table,
+                name: $name,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Rename an arbitrary constraint.
+     */
+    public function renameForeignKey(
+        string $table,
+        string $name,
+        string $newName,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new ForeignKeyRename(
+                table: $table,
+                name: $name,
+                newName: $newName,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Create an INDEX on a table.
+     */
+    public function createIndex(
+        string $table,
+        array $columns,
+        null|string $name = null,
+        null|string $type = null,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new IndexCreate(
+                table: $table,
+                name: $name,
+                columns: $columns,
+                type: $type,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Drop an INDEX from a table.
+     */
+    public function dropIndex(
+        string $table,
+        string $name,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new IndexDrop(
+                table: $table,
+                name: $name,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Rename an arbitrary constraint.
+     */
+    public function renameIndex(
+        string $table,
+        string $name,
+        string $newName,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new IndexRename(
+                table: $table,
+                name: $name,
+                newName: $newName,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Add the PRIMARY KEY constraint on a table.
+     */
+    public function addPrimaryKey(
+        string $table,
+        array $columns,
+        null|string $name = null,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new PrimaryKeyAdd(
+                table: $table,
+                name: $name,
+                columns: $columns,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Drop the PRIMARY KEY constraint from a table.
+     */
+    public function dropPrimaryKey(
+        string $table,
+        string $name,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new PrimaryKeyDrop(
+                table: $table,
+                name: $name,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Drop a table.
+     */
+    public function dropTable(
+        string $name,
+        bool $cascade = false,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new TableDrop(
+                name: $name,
+                cascade: $cascade,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Renames a table.
+     */
+    public function renameTable(
+        string $name,
+        string $newName,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new TableRename(
+                name: $name,
+                newName: $newName,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Create a UNIQUE constraint on a table.
+     */
+    public function addUniqueKey(
+        string $table,
+        array $columns,
+        null|string $name = null,
+        bool $nullsDistinct = true,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new UniqueKeyAdd(
+                table: $table,
+                name: $name,
+                columns: $columns,
+                nullsDistinct: $nullsDistinct,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+
+    /**
+     * Drop a UNIQUE constraint from a table.
+     */
+    public function dropUniqueKey(
+        string $table,
+        string $name,
+        ?string $schema = null,
+    ): static {
+        $this->logChange(
+            new UniqueKeyDrop(
+                table: $table,
+                name: $name,
+                schema: $schema ?? $this->schema,
+                database: $this->database,
+            )
+        );
+
+        return $this;
+    }
+}
diff --git a/src/Schema/Diff/Transaction/NestedSchemaTransaction.php b/src/Schema/Diff/Transaction/NestedSchemaTransaction.php
new file mode 100644
index 0000000..13d3152
--- /dev/null
+++ b/src/Schema/Diff/Transaction/NestedSchemaTransaction.php
@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Transaction;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\SchemaTransaction;
+
+class NestedSchemaTransaction extends AbstractNestedSchemaTransaction
+{
+    public function __construct(
+        private readonly SchemaTransaction $parent,
+        string $database,
+        string $schema,
+        array $conditions = [],
+    ) {
+        parent::__construct($database, $schema, $conditions);
+    }
+
+    /**
+     * Create a table builder.
+     */
+    public function createTable(string $name): NestedTableBuilder
+    {
+        return new NestedTableBuilder(parent: $this, database: $this->database, name: $name, schema: $this->schema);
+    }
+
+    /**
+     * End nested branch and go back to parent.
+     */
+    public function endIf(): SchemaTransaction
+    {
+        return $this->parent;
+    }
+}
diff --git a/src/Schema/Diff/Transaction/NestedTableBuilder.php b/src/Schema/Diff/Transaction/NestedTableBuilder.php
new file mode 100644
index 0000000..0b793e3
--- /dev/null
+++ b/src/Schema/Diff/Transaction/NestedTableBuilder.php
@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Transaction;
+
+/**
+ * @internal
+ *   Exists because PHP has no genericity.
+ */
+class NestedTableBuilder extends AbstractTableBuilder
+{
+    public function __construct(
+        private readonly NestedSchemaTransaction $parent,
+        string $database,
+        string $name,
+        string $schema,
+    ) {
+        parent::__construct($parent, $database, $name, $schema);
+    }
+
+    /**
+     * Table is done.
+     */
+    public function endTable(): NestedSchemaTransaction
+    {
+        $this->createAndLogTable();
+
+        return $this->parent;
+    }
+}
diff --git a/src/Schema/Diff/Transaction/TableBuilder.php b/src/Schema/Diff/Transaction/TableBuilder.php
new file mode 100644
index 0000000..4830af3
--- /dev/null
+++ b/src/Schema/Diff/Transaction/TableBuilder.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Schema\Diff\Transaction;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\SchemaTransaction;
+
+class TableBuilder extends AbstractTableBuilder
+{
+    public function __construct(
+        private readonly SchemaTransaction $parent,
+        string $database,
+        string $name,
+        string $schema,
+    ) {
+        parent::__construct($parent, $database, $name, $schema);
+    }
+
+    /**
+     * Table is done.
+     */
+    public function endTable(): SchemaTransaction
+    {
+        $this->createAndLogTable();
+
+        return $this->parent;
+    }
+}
diff --git a/src/Schema/AbstractObject.php b/src/Schema/Read/AbstractObject.php
similarity index 94%
rename from src/Schema/AbstractObject.php
rename to src/Schema/Read/AbstractObject.php
index 95ae0c9..3f355be 100644
--- a/src/Schema/AbstractObject.php
+++ b/src/Schema/Read/AbstractObject.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace MakinaCorpus\QueryBuilder\Schema;
+namespace MakinaCorpus\QueryBuilder\Schema\Read;
 
 abstract class AbstractObject extends ObjectId
 {
diff --git a/src/Schema/Column.php b/src/Schema/Read/Column.php
similarity index 98%
rename from src/Schema/Column.php
rename to src/Schema/Read/Column.php
index 471757d..4e34613 100644
--- a/src/Schema/Column.php
+++ b/src/Schema/Read/Column.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace MakinaCorpus\QueryBuilder\Schema;
+namespace MakinaCorpus\QueryBuilder\Schema\Read;
 
 class Column extends AbstractObject
 {
diff --git a/src/Schema/ForeignKey.php b/src/Schema/Read/ForeignKey.php
similarity index 97%
rename from src/Schema/ForeignKey.php
rename to src/Schema/Read/ForeignKey.php
index a3edc56..c78b378 100644
--- a/src/Schema/ForeignKey.php
+++ b/src/Schema/Read/ForeignKey.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace MakinaCorpus\QueryBuilder\Schema;
+namespace MakinaCorpus\QueryBuilder\Schema\Read;
 
 final class ForeignKey extends AbstractObject
 {
diff --git a/src/Schema/Key.php b/src/Schema/Read/Key.php
similarity index 95%
rename from src/Schema/Key.php
rename to src/Schema/Read/Key.php
index 70b3b41..1cec736 100644
--- a/src/Schema/Key.php
+++ b/src/Schema/Read/Key.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace MakinaCorpus\QueryBuilder\Schema;
+namespace MakinaCorpus\QueryBuilder\Schema\Read;
 
 class Key extends AbstractObject
 {
diff --git a/src/Schema/ObjectId.php b/src/Schema/Read/ObjectId.php
similarity index 97%
rename from src/Schema/ObjectId.php
rename to src/Schema/Read/ObjectId.php
index aa20157..9c161b0 100644
--- a/src/Schema/ObjectId.php
+++ b/src/Schema/Read/ObjectId.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace MakinaCorpus\QueryBuilder\Schema;
+namespace MakinaCorpus\QueryBuilder\Schema\Read;
 
 class ObjectId
 {
diff --git a/src/Schema/Table.php b/src/Schema/Read/Table.php
similarity index 98%
rename from src/Schema/Table.php
rename to src/Schema/Read/Table.php
index 631c340..e82901d 100644
--- a/src/Schema/Table.php
+++ b/src/Schema/Read/Table.php
@@ -2,7 +2,7 @@
 
 declare(strict_types=1);
 
-namespace MakinaCorpus\QueryBuilder\Schema;
+namespace MakinaCorpus\QueryBuilder\Schema\Read;
 
 use MakinaCorpus\QueryBuilder\Error\QueryBuilderError;
 
diff --git a/src/Schema/SchemaManager.php b/src/Schema/SchemaManager.php
index 57c045a..a73cd7a 100644
--- a/src/Schema/SchemaManager.php
+++ b/src/Schema/SchemaManager.php
@@ -4,14 +4,15 @@
 
 namespace MakinaCorpus\QueryBuilder\Schema;
 
+use MakinaCorpus\QueryBuilder\Error\Bridge\TableDoesNotExistError;
+use MakinaCorpus\QueryBuilder\Error\QueryBuilderError;
+use MakinaCorpus\QueryBuilder\Error\UnsupportedFeatureError;
 use MakinaCorpus\QueryBuilder\Expression;
 use MakinaCorpus\QueryBuilder\ExpressionFactory;
 use MakinaCorpus\QueryBuilder\QueryExecutor;
-use MakinaCorpus\QueryBuilder\Error\QueryBuilderError;
-use MakinaCorpus\QueryBuilder\Error\UnsupportedFeatureError;
-use MakinaCorpus\QueryBuilder\Schema\Diff\AbstractChange;
-use MakinaCorpus\QueryBuilder\Schema\Diff\ChangeLog;
-use MakinaCorpus\QueryBuilder\Schema\Diff\SchemaTransaction;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Browser\ChangeLogBrowser;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Browser\SchemaWriterLogVisitor;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\AbstractChange;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnAdd;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnDrop;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnModify;
@@ -33,18 +34,58 @@
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\TableRename;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyAdd;
 use MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyDrop;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\AbstractCondition;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\ColumnExists;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\IndexExists;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\TableExists;
+use MakinaCorpus\QueryBuilder\Schema\Diff\SchemaTransaction;
+use MakinaCorpus\QueryBuilder\Schema\Read\Column;
+use MakinaCorpus\QueryBuilder\Schema\Read\ForeignKey;
+use MakinaCorpus\QueryBuilder\Schema\Read\Key;
+use MakinaCorpus\QueryBuilder\Schema\Read\Table;
+use Psr\Log\LoggerAwareInterface;
+use Psr\Log\LoggerAwareTrait;
+use Psr\Log\NullLogger;
+
+// @todo Because IDE bug, sorry.
+\class_exists(Column::class);
+\class_exists(ForeignKey::class);
 
 /**
- * Schema alteration SQL statements in this class are mostly standard, but not
- * quite. They basically are the lowest common denominator between PostgreSQL,
- * SQLite and SQLServer. All three are very conservative with SQL standard so
- * basically, the intersection of three is what we have closest to it.
+ * Most SQL here tries to be the closest possible to SQL standard.
+ *
+ * Sadly when it comes to schema introspection, SCHEMATA standard deviates
+ * for every vendor, so there is no real standard here, implementations will
+ * use it for reading because it will at least be resilient against different
+ * versions of the same vendor.
+ *
+ * For writing, most implementations come closer to standard than for schema
+ * introspection, so we can write almost standard SQL in this implementation.
+ * There are a few exceptions, documented along the way, sometime all vendors
+ * have their own dialect, in this case, we almost always prefere PostgreSQL
+ * in this class.
  */
-abstract class SchemaManager
+abstract class SchemaManager implements LoggerAwareInterface
 {
+    use LoggerAwareTrait;
+
     public function __construct(
         protected readonly QueryExecutor $queryExecutor,
-    ) {}
+    ) {
+        $this->setLogger(new NullLogger());
+    }
+
+    /**
+     * Get instance query executor.
+     *
+     * @internal
+     *   In most cases, you should not use this, it will servce for some edge
+     *   cases, such as transaction handling in the schema writer visitor.
+     */
+    public function getQueryExecutor(): QueryExecutor
+    {
+        return $this->queryExecutor;
+    }
 
     /**
      * Does this platform supports DDL transactions.
@@ -159,16 +200,13 @@ protected abstract function getTableReverseForeignKeys(string $database, string
     public function modify(string $database, string $schema = 'public'): SchemaTransaction
     {
         return new SchemaTransaction(
-            $this,
             $database,
             $schema,
-            function (ChangeLog $changeLog) {
-                // @todo start transaction
-                foreach ($changeLog->getAll() as $change) {
-                    $this->apply($change);
-                }
-                // @todo end transaction
-            }
+            function (SchemaTransaction $transaction) {
+                $browser = new ChangeLogBrowser();
+                $browser->addVisitor(new SchemaWriterLogVisitor($this));
+                $browser->browse($transaction);
+            },
         );
     }
 
@@ -249,7 +287,7 @@ protected function columnModifyToAdd(ColumnModify $change): ColumnAdd
      * @todo
      *   Maybe later, some normalization here with characters sets.
      */
-    protected function writeColumnSpecCollation(string $collation): Expression
+    protected function doWriteColumnCollation(string $collation): Expression
     {
         return $this->raw('COLLATE ?::id', $collation);
     }
@@ -264,7 +302,7 @@ protected function writeColumnSpecCollation(string $collation): Expression
      *     - but there might be constants (such as CURRENT_TIME for example),
      *     - or function calls!
      */
-    protected function writeColumnSpecDefault(string $type, string $default): Expression
+    protected function doWriteColumnDefault(string $type, string $default): Expression
     {
         return match ($type) {
             default => $this->raw($default),
@@ -278,7 +316,7 @@ protected function writeColumnSpecDefault(string $type, string $default): Expres
      *   Here, we might want to plug over the converter in order to normalize
      *   type depending upon the RDBMS.
      */
-    protected function writeColumnSpecType(ColumnAdd|ColumnModify $change): Expression
+    protected function doWriteColumnType(ColumnAdd|ColumnModify $change): Expression
     {
         if (!$type = $change->getType()) {
             throw new QueryBuilderError("You cannot change collation without specifying a new type.");
@@ -288,7 +326,7 @@ protected function writeColumnSpecType(ColumnAdd|ColumnModify $change): Expressi
         $pieces = [$this->raw($type)];
 
         if ($collation = $change->getCollation()) {
-            $pieces[] = $this->writeColumnSpecCollation($collation);
+            $pieces[] = $this->doWriteColumnCollation($collation);
         }
 
         return $this->raw(\implode(' ', \array_fill(0, \count($pieces), '?')), [...$pieces]);
@@ -299,7 +337,7 @@ protected function writeColumnSpecType(ColumnAdd|ColumnModify $change): Expressi
      *
      * Column specification.
      */
-    protected function writeColumnSpec(ColumnAdd $change): Expression
+    protected function doWriteColumn(ColumnAdd $change): Expression
     {
         $pieces = [];
 
@@ -308,14 +346,14 @@ protected function writeColumnSpec(ColumnAdd $change): Expression
         }
 
         if ($default = $change->getDefault()) {
-            $this->raw('DEFAULT ?', [$default]);
+            $this->raw('DEFAULT ?', [$this->doWriteColumnDefault($change->getType(), $default)]);
         }
 
         return $this->raw(
             '?::id ? ' . \implode(' ', \array_fill(0, \count($pieces), '?')),
             [
                 $change->getName(),
-                $this->writeColumnSpecType($change),
+                $this->doWriteColumnType($change),
                 ...$pieces,
             ],
         );
@@ -328,7 +366,7 @@ protected function writeColumnSpec(ColumnAdd $change): Expression
      */
     protected function writeColumnAdd(ColumnAdd $change): iterable|Expression
     {
-        return $this->raw('ALTER TABLE ? ADD COLUMN ?', [$this->table($change), $this->writeColumnSpec($change)]);
+        return $this->raw('ALTER TABLE ? ADD COLUMN ?', [$this->table($change), $this->doWriteColumn($change)]);
     }
 
     /**
@@ -365,7 +403,7 @@ protected function writeColumnModify(ColumnModify $change): iterable|Expression
         }
 
         if ($change->getType() || $change->getCollation()) {
-            $pieces[] = $this->raw('ALTER COLUMN ?::id TYPE ?', [$name, $this->writeColumnSpecType($change)]);
+            $pieces[] = $this->raw('ALTER COLUMN ?::id TYPE ?', [$name, $this->doWriteColumnType($change)]);
         }
 
         if (null !== ($nullable = $change->isNullable())) {
@@ -418,7 +456,7 @@ protected function writeColumnRename(ColumnRename $change): iterable|Expression
      *
      * Constraint specification.
      */
-    protected function writeConstraintSpec(?string $name, Expression $spec): Expression
+    protected function doWriteConstraint(?string $name, Expression $spec): Expression
     {
         if ($name) {
             return $this->raw('CONSTRAINT ?::id ?', [$name, $spec]);
@@ -433,7 +471,7 @@ protected function writeConstraintSpec(?string $name, Expression $spec): Express
      *
      * @todo SQLite does not support this and requires a table copy.
      */
-    protected function writeConstraintDropSpec(string $name, string $table, string $schema): Expression
+    protected function doWriteConstraintDrop(string $name, string $table, string $schema): Expression
     {
         return $this->raw('ALTER TABLE ? DROP CONSTRAINT ?::id', [$this->table($table, $schema), $name]);
     }
@@ -445,7 +483,7 @@ protected function writeConstraintDropSpec(string $name, string $table, string $
      */
     protected function writeConstraintDrop(ConstraintDrop $change): iterable|Expression
     {
-        return $this->writeConstraintDropSpec($change->getName(), $change->getTable(), $change->getSchema());
+        return $this->doWriteConstraintDrop($change->getName(), $change->getTable(), $change->getSchema());
     }
 
     /**
@@ -471,7 +509,7 @@ protected function writeConstraintRename(ConstraintRename $change): iterable|Exp
     /**
      * Write the "CASCADE|NO ACTION|RESTRICT|SET DEFAULT|SET NULL" FOREIGN KEY clause.
      */
-    protected function writeForeignKeySpecBehavior(string $behavior): Expression
+    protected function doWriteForeignKeyBehavior(string $behavior): Expression
     {
         return match ($behavior) {
             ForeignKeyAdd::ON_DELETE_CASCADE, ForeignKeyAdd::ON_UPDATE_CASCADE => $this->raw('CASCADE'),
@@ -485,7 +523,7 @@ protected function writeForeignKeySpecBehavior(string $behavior): Expression
     /**
      * Write the "INITIALLY DEFERRED|IMMEDIATE" FOREIGN KEY clause.
      */
-    protected function writeForeignKeySpecInitially(string $initially): Expression
+    protected function doWriteForeignKeyInitially(string $initially): Expression
     {
         return match ($initially) {
             ForeignKeyAdd::INITIALLY_DEFERRED, ForeignKeyAdd::INITIALLY_DEFERRED => $this->raw('INITIALLY DEFERRED'),
@@ -498,14 +536,14 @@ protected function writeForeignKeySpecInitially(string $initially): Expression
      *
      * Foreign key constraint specification.
      */
-    protected function writeForeignKeySpec(ForeignKeyAdd $change): Expression
+    protected function doWriteForeignKey(ForeignKeyAdd $change): Expression
     {
         $suffix = [];
         if ($deleteBehaviour = $change->getOnDelete()) {
-            $suffix[] = $this->raw('ON DELETE ?', $this->writeForeignKeySpecBehavior($deleteBehaviour));
+            $suffix[] = $this->raw('ON DELETE ?', $this->doWriteForeignKeyBehavior($deleteBehaviour));
         }
         if ($updateBehaviour = $change->getOnUpdate()) {
-            $suffix[] = $this->raw('ON UPDATE ?', $this->writeForeignKeySpecBehavior($updateBehaviour));
+            $suffix[] = $this->raw('ON UPDATE ?', $this->doWriteForeignKeyBehavior($updateBehaviour));
         }
         if ($change->isDeferrable()) {
             $suffix[] = $this->raw('DEFERRABLE');
@@ -513,10 +551,10 @@ protected function writeForeignKeySpec(ForeignKeyAdd $change): Expression
             $suffix[] = $this->raw('NOT DEFERRABLE');
         }
         if ($initially = $change->getInitially()) {
-            $suffix[] = $this->writeForeignKeySpecInitially($initially);
+            $suffix[] = $this->doWriteForeignKeyInitially($initially);
         }
 
-        return $this->writeConstraintSpec(
+        return $this->doWriteConstraint(
             $change->getName(),
             $this->raw(
                 'FOREIGN KEY (?::id[]) REFERENCES ? (?::id[]) ' . \implode('', \array_fill(0, \count($suffix), ' ?')),
@@ -537,7 +575,7 @@ protected function writeForeignKeySpec(ForeignKeyAdd $change): Expression
      */
     protected function writeForeignKeyAdd(ForeignKeyAdd $change): iterable|Expression
     {
-        return $this->raw('ALTER TABLE ? ADD ?', [$this->table($change), $this->writeForeignKeySpec($change)]);
+        return $this->raw('ALTER TABLE ? ADD ?', [$this->table($change), $this->doWriteForeignKey($change)]);
     }
 
     /**
@@ -557,7 +595,7 @@ protected function writeForeignKeyModify(ForeignKeyModify $change): iterable|Exp
      */
     protected function writeForeignKeyDrop(ForeignKeyDrop $change): iterable|Expression
     {
-        return $this->writeConstraintDropSpec($change->getName(), $change->getTable(), $change->getSchema());
+        return $this->doWriteConstraintDrop($change->getName(), $change->getTable(), $change->getSchema());
     }
 
     /**
@@ -619,7 +657,7 @@ protected function writeIndexRename(IndexRename $change): iterable|Expression
      */
     protected function writePrimaryKeyAdd(PrimaryKeyAdd $change): iterable|Expression
     {
-        return $this->raw('ALTER TABLE ? ADD ?', [$this->table($change), $this->writePrimaryKeySpec($change)]);
+        return $this->raw('ALTER TABLE ? ADD ?', [$this->table($change), $this->doWritePrimaryKey($change)]);
     }
 
     /**
@@ -631,15 +669,15 @@ protected function writePrimaryKeyAdd(PrimaryKeyAdd $change): iterable|Expressio
      */
     protected function writePrimaryKeyDrop(PrimaryKeyDrop $change): iterable|Expression
     {
-        return $this->writeConstraintDropSpec($change->getName(), $change->getTable(), $change->getSchema());
+        return $this->doWriteConstraintDrop($change->getName(), $change->getTable(), $change->getSchema());
     }
 
     /**
      * Override if standard SQL is not enough.
      */
-    protected function writePrimaryKeySpec(PrimaryKeyAdd $change): Expression
+    protected function doWritePrimaryKey(PrimaryKeyAdd $change): Expression
     {
-        return $this->writeConstraintSpec(
+        return $this->doWriteConstraint(
             $change->getName(),
             $this->raw('PRIMARY KEY (?::id[])', [$change->getColumns()]),
         );
@@ -648,7 +686,7 @@ protected function writePrimaryKeySpec(PrimaryKeyAdd $change): Expression
     /**
      * Override if standard SQL is not enough.
      */
-    protected function writeTableCreateSpecUniqueKey(UniqueKeyAdd $change): Expression
+    protected function doWriteTableCreateUniqueKey(UniqueKeyAdd $change): Expression
     {
         if (!$change->isNullsDistinct()) {
             // @todo Implement this with PostgreSQL.
@@ -657,7 +695,7 @@ protected function writeTableCreateSpecUniqueKey(UniqueKeyAdd $change): Expressi
 
         $spec = $this->raw('UNIQUE (?::id[])', [$change->getColumns()]);
 
-        return $this->writeConstraintSpec($change->getName(), $spec);
+        return $this->doWriteConstraint($change->getName(), $spec);
     }
 
     /**
@@ -667,15 +705,15 @@ protected function writeTableCreateSpecUniqueKey(UniqueKeyAdd $change): Expressi
      */
     protected function writeTableCreate(TableCreate $change): iterable|Expression
     {
-        $pieces = \array_map($this->writeColumnSpec(...), $change->getColumns());
+        $pieces = \array_map($this->doWriteColumn(...), $change->getColumns());
         if ($primaryKey = $change->getPrimaryKey()) {
-            $pieces[] = $this->writePrimaryKeySpec($primaryKey);
+            $pieces[] = $this->doWritePrimaryKey($primaryKey);
         }
         foreach ($change->getUniqueKeys() as $uniqueKey) {
-            $pieces[] = $this->writeTableCreateSpecUniqueKey($uniqueKey);
+            $pieces[] = $this->doWriteTableCreateUniqueKey($uniqueKey);
         }
         foreach ($change->getForeignKeys() as $foreignKey) {
-            $pieces[] = $this->writeForeignKeySpec($foreignKey);
+            $pieces[] = $this->doWriteForeignKey($foreignKey);
         }
 
         $placeholder = \implode(', ', \array_fill(0, \count($pieces), '?'));
@@ -747,10 +785,68 @@ protected function writeUniqueKeyDrop(UniqueKeyDrop $change): iterable|Expressio
         return $this->raw('DROP INDEX ?::id', [$change->getName()]);
     }
 
+    /**
+     * Override if standard SQL is not enough.
+     */
+    protected function evaluateConditionColumnExists(ColumnExists $condition): bool
+    {
+        try {
+            return \in_array(
+                $condition->getColumn(),
+                $this
+                    ->getTable(
+                        $condition->getDatabase(),
+                        $condition->getTable(),
+                        $condition->getSchema()
+                    )
+                    ->getColumnNames()
+            );
+        } catch (TableDoesNotExistError) {
+            return false;
+        }
+    }
+
+    /**
+     * Override if standard SQL is not enough.
+     */
+    protected function evaluateConditionIndexExists(IndexExists $condition): bool
+    {
+        throw new UnsupportedFeatureError("Not implemented yet.");
+    }
+
+    /**
+     * Override if standard SQL is not enough.
+     */
+    protected function evaluateConditionTableExists(TableExists $condition): bool
+    {
+        return $this->tableExists($condition->getDatabase(), $condition->getTable(), $condition->getSchema());
+    }
+
+    /**
+     * Condition evualation.
+     *
+     * @internal
+     *   For SchemaWriterLogVisitor usage only.
+     */
+    public function evaluateCondition(AbstractCondition $condition): bool
+    {
+        $matches = (bool) match (\get_class($condition)) {
+            ColumnExists::class => $this->evaluateConditionColumnExists($condition),
+            IndexExists::class => $this->evaluateConditionIndexExists($condition),
+            TableExists::class => $this->evaluateConditionTableExists($condition),
+            default => throw new QueryBuilderError(\sprintf("Unsupported condition: %s", \get_class($condition))),
+        };
+
+        return $condition->isNegation() ? !$matches : $matches;
+    }
+
     /**
      * Apply a given change in the current schema.
+     *
+     * @internal
+     *   For SchemaWriterLogVisitor usage only.
      */
-    protected function apply(AbstractChange $change): void
+    public function applyChange(AbstractChange $change): void
     {
         $expressions = match (\get_class($change)) {
             ColumnAdd::class => $this->writeColumnAdd($change),
@@ -777,16 +873,6 @@ protected function apply(AbstractChange $change): void
             default => throw new QueryBuilderError(\sprintf("Unsupported alteration operation: %s", \get_class($change))),
         };
 
-        $this->executeChange($change, $expressions);
-    }
-
-    /**
-     * Really execute the change.
-     *
-     * @param Expression|iterable<Expression> $expressions
-     */
-    protected function executeChange(AbstractChange $change, iterable|Expression $expressions): void
-    {
         foreach (\is_iterable($expressions) ? $expressions : [$expressions] as $expression) {
             $this->queryExecutor->executeStatement($expression);
         }
diff --git a/tests/Platform/Schema/AbstractSchemaTestCase.php b/tests/Platform/Schema/AbstractSchemaTestCase.php
index 6d41787..826f4aa 100644
--- a/tests/Platform/Schema/AbstractSchemaTestCase.php
+++ b/tests/Platform/Schema/AbstractSchemaTestCase.php
@@ -4,11 +4,11 @@
 
 namespace MakinaCorpus\QueryBuilder\Tests\Platform\Schema;
 
-use MakinaCorpus\QueryBuilder\Platform;
+use MakinaCorpus\QueryBuilder\Error\Bridge\TableDoesNotExistError;
 use MakinaCorpus\QueryBuilder\Error\QueryBuilderError;
 use MakinaCorpus\QueryBuilder\Error\UnsupportedFeatureError;
-use MakinaCorpus\QueryBuilder\Error\Bridge\TableDoesNotExistError;
-use MakinaCorpus\QueryBuilder\Schema\ForeignKey;
+use MakinaCorpus\QueryBuilder\Platform;
+use MakinaCorpus\QueryBuilder\Schema\Read\ForeignKey;
 use MakinaCorpus\QueryBuilder\Schema\SchemaManager;
 use MakinaCorpus\QueryBuilder\Tests\FunctionalTestCase;
 
@@ -935,6 +935,62 @@ public function testUniqueKeyDrop(): void
         self::expectNotToPerformAssertions();
     }
 
+    public function testIfTableExists(): void
+    {
+        $this
+            ->getSchemaManager()
+            ->modify('test_db')
+                ->ifTableExists('org')
+                    ->addColumn('org', 'if_added_col', 'text', true)
+                ->endIf()
+                ->ifTableNotExists('org')
+                    ->addColumn('org', 'if_not_added_col', 'text', true)
+                ->endIf()
+            ->commit()
+        ;
+
+        $columnNames = $this
+            ->getSchemaManager()
+            ->getTable('test_db', 'org')
+            ->getColumnNames()
+        ;
+
+        self::assertContains('if_added_col', $columnNames);
+        self::assertNotContains('if_not_added_col', $columnNames);
+    }
+
+    public function testIfColumnExists(): void
+    {
+        $this
+            ->getSchemaManager()
+            ->modify('test_db')
+                ->ifColumnExists('org', 'role')
+                    ->addColumn('org', 'if_added_col_2', 'text', true)
+                ->endIf()
+                ->ifColumnNotExists('org', 'role')
+                    ->addColumn('org', 'if_not_added_col_2', 'text', true)
+                ->endIf()
+                ->ifColumnExists('org', 'role_nope')
+                    ->addColumn('org', 'if_added_col_3', 'text', true)
+                ->endIf()
+                ->ifColumnNotExists('org', 'role_nope')
+                    ->addColumn('org', 'if_not_added_col_3', 'text', true)
+                ->endIf()
+            ->commit()
+        ;
+
+        $columnNames = $this
+            ->getSchemaManager()
+            ->getTable('test_db', 'org')
+            ->getColumnNames()
+        ;
+
+        self::assertContains('if_added_col_2', $columnNames);
+        self::assertNotContains('if_not_added_col_2', $columnNames);
+        self::assertNotContains('if_added_col_3', $columnNames);
+        self::assertContains('if_not_added_col_3', $columnNames);
+    }
+
     public function testListTables(): void
     {
         $tables = $this->getSchemaManager()->listTables('test_db');
diff --git a/tests/Schema/SchemaTransactionTest.php b/tests/Schema/SchemaTransactionTest.php
new file mode 100644
index 0000000..27c8687
--- /dev/null
+++ b/tests/Schema/SchemaTransactionTest.php
@@ -0,0 +1,106 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MakinaCorpus\QueryBuilder\Tests\Schema;
+
+use MakinaCorpus\QueryBuilder\Schema\Diff\Browser\ChangeLogBrowser;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Browser\ChangeLogVisitor;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Change\AbstractChange;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\AbstractCondition;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Condition\ColumnExists;
+use MakinaCorpus\QueryBuilder\Schema\Diff\SchemaTransaction;
+use MakinaCorpus\QueryBuilder\Schema\Diff\Transaction\AbstractNestedSchemaTransaction;
+use PHPUnit\Framework\TestCase;
+
+class SchemaTransactionTest extends TestCase
+{
+    public function testNesting(): void
+    {
+        $transaction = new SchemaTransaction('some_db', 'some_schema', fn () => null);
+
+        $transaction
+            ->ifTableNotExists('users')
+                ->createTable('users')
+                    ->column('id', 'serial', false)
+                    ->primaryKey(['id'])
+                ->endTable()
+            ->endIf()
+            ->ifColumnNotExists('users', 'email')
+                ->ifColumnNotExists('users', 'email')
+                    ->addColumn('users', 'email', 'text', true)
+                ->endIf()
+                ->ifColumnExists('users', 'skip')
+                    ->addColumn('users', 'email', 'text', true)
+                ->endIf()
+                ->addUniqueKey('users', ['email'])
+            ->endIf()
+            ->addColumn('users', 'name', 'text', false)
+            ->commit()
+        ;
+
+        $visitor = new class () extends ChangeLogVisitor
+        {
+            private array $lines = [];
+
+            #[\Override]
+            public function enter(AbstractNestedSchemaTransaction $nested, int $depth): void
+            {
+                $this->lines[] = "Entering level " . $depth;
+            }
+
+            #[\Override]
+            public function leave(AbstractNestedSchemaTransaction $nested, int $depth): void
+            {
+                $this->lines[] = "Exiting level " . $depth;
+            }
+
+            #[\Override]
+            public function skip(AbstractNestedSchemaTransaction $nested, int $depth): void
+            {
+                $this->lines[] = "Skipping level " . $depth;
+            }
+
+            #[\Override]
+            public function evaluate(AbstractCondition $condition): bool
+            {
+                if ($condition instanceof ColumnExists && 'skip' === $condition->getColumn()) {
+                    return false;
+                }
+                return true;
+            }
+
+            #[\Override]
+            public function apply(AbstractChange $change): void
+            {
+                $this->lines[] = "Applying " . \get_class($change);
+            }
+
+            public function getOutput(): string
+            {
+                return \implode("\n", $this->lines);
+            }
+        };
+
+        $browser = new ChangeLogBrowser();
+        $browser->addVisitor($visitor);
+        $browser->browse($transaction);
+
+        self::assertSame(
+            $visitor->getOutput(),
+            <<<EOT
+            Entering level 1
+            Applying MakinaCorpus\QueryBuilder\Schema\Diff\Change\TableCreate
+            Exiting level 1
+            Entering level 1
+            Entering level 2
+            Applying MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnAdd
+            Exiting level 2
+            Skipping level 2
+            Applying MakinaCorpus\QueryBuilder\Schema\Diff\Change\UniqueKeyAdd
+            Exiting level 1
+            Applying MakinaCorpus\QueryBuilder\Schema\Diff\Change\ColumnAdd
+            EOT,
+        );
+    }
+}