一、分组查询
二、多表查询
等值连接
select d.deptno,d.dname,count(e.empno)
from emp e,dept d
where e.deptno = d.deptno
group by d.deptno,d.dname:
不等值连接
select d.deptno,d.dname,count(e.empno)
from emp e,dept d
where e.deptno d.deptno
group by de.sal between .deptno and d.dname:
外连接
select d.deptno,d.dname,count(e.empno)
from emp e,dept d
where e.deptno = d.deptno(+)
group by d.deptno,d.dname:
自连接(核心是把一张表命名成两个名字)
select e.ename 员工姓名,b.ename 老板姓名
from emp e, emo b
where e.mgr = b.empno
三、子查询
select level,ename,sal,mgr
from emp
connect by prior empno = mgr
start with empno = 7839
connect by
from(select rownum r,empno,ename,sal)
from ()