Why do QA engineers need SQL skills?

The UI only shows you what the application chooses to display. SQL gives you direct access to the source of truth: the database. Common QA uses include:

Validating data persistence — after submitting a form, confirm the row exists with the correct values, not just that a success message appeared.

Setting up test data — INSERT or UPDATE records to reach a specific precondition faster than clicking through the UI.

Tearing down test data — DELETE the records your test created so the next run starts clean.

Finding bugs the UI hides — soft-deleted records still appearing, orphaned foreign keys, duplicate rows from a race condition, NULL values where NOT NULL was expected.

Comparing expected vs actual — join a "results" table against an "expected" table and SELECT rows where they differ.

Most QA roles at mid-level and above expect at least read fluency (SELECT, JOIN, WHERE, GROUP BY). SDET and automation roles often expect the full CRUD set.