select * from scott.emp where deptno in (select deptno from scott.dept where dname='SALES');
select * from scott.emp where exists (select 1 from scott.dept where emp.deptno=dept.deptno and dname='SALES')

--删除表中的重复值（主要是弄清rowid）
?delete from emp_bak e
? where e.rowid >
??????? (select min(x.rowid) from emp_bak x where x.empno = e.empno)

? delete from emp_bak
?? where rowid not in (select max(rowid) from emp_bak group by empno)

? select *? from emp_bak
?? where empno? in (select empno from emp_bak group by empno)

select t.rowid, t.* from emp_bak t


select * from emp_bak

create table emp_bak1
as select * from emp_bak


select * from emp_bak1

update emp_bak1 set sal = sal + 1000

update emp_bak1 set comm = nvl(comm ,0 ) + 500

?

把一个表的值覆盖另一个表中的值
? update emp_bak b
???? set b.sal =
???????? (select sal from emp_bak1 a where a.empno = b.empno),
???????? b.comm =
???????? (select comm from emp_bak1 a where a.empno = b.empno)

?

?

?