表A
ID NAME
1 A1
2 A2
3 A3
表B
ID AID NAME
1 1 B1
2 2 B2
3 2 B3
SELECT ID,NAME FROM A WHERE EXIST (SELECT * FROM B WHERE A.ID=B.AID)
等价于 select id.name from A where A.ID IN (SELECT B.ID FROM B)
执行结果为
1 A1
2 A2
NOT EXISTS 就是反过来
SELECT ID,NAME FROM A WHERE NOT EXIST (SELECT * FROM B WHERE A.ID=B.AID)
执行结果为
3 A3
应用场景：
--不等于
select * from udf_user u where not exists (
select * from armc_user_team t where t.user_name=u.username_ and t.team_code='DCCDJP'
)
--同时存在
select * from armc_user_team t where t.team_code='a'
and exists(select * from armc_user_team t1 where t1.user_name=t.user_name and t1.team_code='b')