SQLGlot as a SQL Compatibility Test Harness

SQL translation is not the hard part. Proving that translated SQL still means the same thing is the hard part.

The practical problem

SQLGlot is useful for parsing, transpiling, and inspecting SQL across dialects. In migration work, teams often treat that as a one-time helper. That misses the bigger ODI pattern.

SQL compatibility should become a test harness. Every time a model, query, engine version, or dialect rule changes, the harness should show what still parses, what still executes, and what still returns equivalent meaning.

What the harness tests

Start with parser coverage. The harness should list which production queries parse successfully, which constructs require manual review, and which dialect assumptions appear most often.

Then test transpilation. A query that converts syntactically can still change behavior around date math, null handling, quoting, arrays, structs, window functions, or type coercion. Each of those deserves examples.

Finally, test semantic equivalence against representative data. The test does not need to prove every historical query forever. It needs to prove the important contracts for the models and workloads being migrated.

What breaks first

• Teams count successful transpilation as migration success without result comparison.
• Unsupported dialect features become scattered manual fixes with no regression test.
• Test data lacks the edge cases that reveal null, timezone, or type behavior.
• Lineage and ownership context get lost while query syntax is being repaired.

Questions to ask

Use these questions when SQLGlot supports a platform migration.

• Which queries are parsed, transpiled, executed, and result-checked?
• Which dialect features require manual review?
• Which edge cases prove semantic behavior?
• Can the harness run in CI against representative fixtures?
• Can lineage show which business assets depend on each migrated query?

For broader migration discipline, read Migrating the Semantic Layer to Open Infrastructure, The Strangler-Fig Pattern for Data Platform Migration, and ODI vs Modern Data Stack.

Sources to start with

Use SQLGlot for language evidence and the platform docs for execution evidence. Both are required.

• SQLGlot documentation
• Apache Iceberg table specification
• dbt Core documentation
• OpenLineage documentation