$--- title: UPDATE-to-SELECT Conversion outline: deep

UPDATE ? SELECT Conversion

UpdateResultSelectConverter mirrors the update semantics by rewiring the SET expressions and predicate filters into a read-only query. This makes it possible to assert returning rows or row counts without touching a live table while keeping the semantics of joins, FROM sources, and WHERE predicates intact.

Conversion workflow

1. Rewrite the SET clause expressions so the requested return columns either emit the updated expressions or fall back to existing column references.
2. Attach the original FROM sources and WHERE predicate to the new select so the same rows are targeted.
3. Expand RETURNING * when a table definition is supplied, and emit SELECT count(*) AS "count" when no RETURNING clause exists.
4. Detach any user-defined WITH clause, ensure fixture coverage for the referenced tables, and prepend the fixture CTEs back into the result so the final SELECT only touches fixtures.

Fixtures and joins

The converter needs fixtureTables for every table that appears in the FROM clause, including UPDATE ... FROM targets. By default, missing fixtures raise an error, but you can switch to warn or passthrough when you are still composing coverage. FixtureCteBuilder takes those definitions and injects them ahead of the rewritten select so each table (target or helper) resolves to its fixture rows.

Missing fixture strategy

Use the missingFixtureStrategy option to control how strict the converter is. error (the default) enforces coverage, warn logs the uncovered table without stopping the conversion, and passthrough leaves the table reference alone so you can integrate against an external database when needed.

When to read this doc

• You are investigating why the update converter reports a missing fixture for the target or one of the joined tables.
• You want to understand how returning expressions like price + 10 survive the translation.
• You need to pair the select with fixture definitions so the converter can run in a fixture-only test harness.

Learn more

• UpdateResultSelectConverter API
• Select-Centered Philosophy for the rationale behind read-only assertions.
• SQLite Testkit Guide to see how fixtures feed into the rewritten select.