select a value where it doesn't exist in another table

Question

I have two tables

Table A:

ID
1
2
3
4

Table B:

ID
1
2
3

I have two requests:

• I want to

Answer 1

This would select 4 in your case

SELECT ID FROM TableA WHERE ID NOT IN (SELECT ID FROM TableB)

This would delete them

DELETE FROM TableA WHERE ID NOT IN (SELECT ID FROM TableB)