oracle union intersect minus

---并，交，差集
---虽然有时候可以用in等代替

---union ,union all,minus,intersect

create table t1 as  select 1 as id from dual union select 2 as id from dual union select 3 as id from dual
create table t2 as  select 1 as id from dual union select 4 as id from dual union select 5 as id from dual

select * from t1 union select * from t2
1
2
3
4
5


select * from t1 union all select * from t2
1
2
3
1
4
5

select * from t1 minus select * from t2
2
3

select * from t2 minus select * from t1
4
5

select * from t2 intersect select * from t1

1