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)

Question

SQL Fundamentals — Hard

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)

Accepted Answer

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.