SQL
Find Records Without a Match in Another Table
Discover how to efficiently query records from one SQL table that do not have a matching entry in a related table, using LEFT JOIN and WHERE IS NULL.
SELECT
A.id, A.name
FROM
TableA A
LEFT JOIN
TableB B ON A.id = B.tableA_id
WHERE
B.tableA_id IS NULL;
How it works: This SQL snippet demonstrates an 'anti-join' pattern. It uses a `LEFT JOIN` to combine rows from `TableA` with matching rows from `TableB`. By filtering `WHERE B.tableA_id IS NULL`, it effectively selects only those rows from `TableA` for which no corresponding entry was found in `TableB`, identifying orphaned records or missing relationships.