Create redshift limit one macro

[fivetran-avinash]

PR Overview

This PR will address the following Issue/Feature: Internal ticket

This PR will result in the following new package version:

v0.15.0 - staging model results will be different for redshift users potentially (1 row instead of 0 for empty rows)

Please provide the finalized CHANGELOG entry which details the relevant changes included in this PR:

Under the Hood

• (Affects Redshift only) Creates new shopify_union_data macro to accommodate Redshift's treatment of empty tables.
  • For each staging model, if the source table is not found in any of your schemas, the package will create a empty table with 0 rows for non-Redshift warehouses and a table with 1 all-null row for Redshift destinations.
  • This is necessary as Redshift will ignore explicit data casts when a table is completely empty and materialize every column as a varchar. This throws errors in downstream transformations in the shopify package. The 1 row will ensure that Redshift will respect the package's datatype casts.

PR Checklist

Basic Validation

Please acknowledge that you have successfully performed the following commands locally:

• dbt run –full-refresh && dbt test
• [NA] dbt run (if incremental models are present) && dbt test

Before marking this PR as "ready for review" the following have been applied:

• [NA] The appropriate issue has been linked, tagged, and properly assigned
• All necessary documentation and version upgrades have been applied
• docs were regenerated (unless this PR does not include any code or yml updates)
• BuildKite integration tests are passing
• [NA] Detailed validation steps have been provided below

Detailed Validation

Please share any and all of your validation steps:

See concurrent transform PR.

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