What does the following pattern detect? SELECT a.id FROM tableA a WHERE NOT EXISTS (SELECT 1 FROM tableB b WHERE b.a

Explanation

This pattern detects rows in tableA that do not have corresponding rows in tableB. It uses the NOT EXISTS clause to filter out rows where a matching row in tableB does not exist.

Key points

The query checks for absence of matching rows in tableB
It uses a subquery to compare values between tables
The result is a list of rows from tableA without matches in tableB

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What does the following pattern detect? SELECT a.id FROM tableA a WHERE NOT EXISTS (SELECT 1 FROM tableB b WHERE b.a_id = a.id)