Question

**Table A**
1
2
3
4
5
6


**Table B**
2
3
5

How can I select for entry IDs that only exist in Table B? In this example, I’m looking for a query that returns 1, 4, and 6.

Answer 1

Assuming the column is named ‘id’, either:

SELECT *
FROM tableA a
WHERE NOT EXISTS (SELECT 1 FROM tableB WHERE id = a.id)

or

SELECT *
FROM TableA
WHERE id NOT IN (SELECT id FROM tableB)

You will probably need to test to see which performs best. MySQL can be a bit unpredictable.