a-b 차집합 구하기

select tableA.id, tableA.name from tableA LEFT JOIN tableB ON table A.id=tableB.id WHERE tableB.id IS NULL;

b-a 차집합 구하기
select tableA.id, tableA.name from tableA LEFT JOIN tableB ON table A.id=tableB.id WHERE tableA.id IS NULL;

* 참고 흔히 행하는 잘못된 쿼리
select tableA.id, tableA.name from tableA LEFT JOIN tableB ON tableA.id=tableB.id WHERE tableB.id IS NULL;