/*
语法1：
select *
from tab1,tab2
where 条件;
语法2：
select *
from tab1 inner join tab2
on 条件;
内连接查询效果： 只有满足条件的数据才会显示。
*/
-- 笛卡尔积 = 14*4= 56
-- 需求：查询员工和部门数据
select *
from emp,dept;
-- 需求：查询员工和部门数据
-- 语法1
selecte.empno,e.ename,d.deptno,d.dname
from emp e,dept d
where e.deptno = d.deptno;
-- 语法2
selecte.empno,e.ename,d.deptno,d.dname
from emp e innerjoin dept d
on e.deptno = d.deptno;
-- 案例
-- 需求：查询员工及其上司信息
select e1.empno,e1.ename,e2.empno,e2.ename
from emp e1,emp e2
where e1.mgr = e2.empno;
-- 需求：在上面基础上，查询员工的部门信息
selecte1.empno,e1.ename,d1.deptno,d1.dname,e2.empno,e2.ename
from emp e1,emp e2,dept d1
where e1.mgr = e2.empno
and e1.deptno = d1.deptno;
-- 需求：在上面基础上，查询上司的部门信息
selecte1.empno,e1.ename,d1.deptno,d1.dname,e2.empno,e2.ename,d2.deptno,d2.dname
from emp e1,emp e2,dept d1,dept d2
where e1.mgr = e2.empno
and e1.deptno = d1.deptno
and e2.deptno = d2.deptno;
-- 需求：在上面基础上，查询员工的工资级别
selecte1.empno,e1.ename,d1.deptno,d1.dname,e1.sal,s1.grade,e2.empno,e2.ename,d2.deptno,d2.dname
from emp e1,emp e2,dept d1,deptd2,salgrade s1
where e1.mgr = e2.empno
and e1.deptno = d1.deptno
and e2.deptno = d2.deptno
and e1.sal between s1.losal and s1.hisal;
-- 需求：在上面基础上，查询上司的工资级别
select e1.empno,e1.ename,d1.deptno,d1.dname,e1.sal,s1.grade,e2.empno,e2.ename,d2.deptno,d2.dname,e2.sal,s2.grade
from emp e1,emp e2,dept d1,deptd2,salgrade s1,salgrade s2
where e1.mgr = e2.empno
and e1.deptno = d1.deptno
and e2.deptno = d2.deptno
and e1.sal between s1.losal and s1.hisal
and e2.sal between s2.losal and s2.hisal;
-- 需求：在上面基础上，把员工的工资级别显示为"一级，二级，三级...."
selecte1.empno,e1.ename,d1.deptno,d1.dname,e1.sal,
decode(s1.grade,1,'一级',2,'二级',3,'三级',4,'四级') as员工工资级别
,e2.empno,e2.ename,d2.deptno,d2.dname,e2.sal,s2.grade
from emp e1,emp e2,dept d1,deptd2,salgrade s1,salgrade s2
where e1.mgr = e2.empno
and e1.deptno = d1.deptno
and e2.deptno = d2.deptno
and e1.sal between s1.losal and s1.hisal
and e2.sal between s2.losal and s2.hisal;
-- 需求：在上面基础上，把上司的工资级别显示为"一级，二级，三级...."
selecte1.empno,e1.ename,d1.deptno,d1.dname,e1.sal,
decode(s1.grade,1,'一级',2,'二级',3,'三级',4,'四级') as员工工资级别
,e2.empno,e2.ename,d2.deptno,d2.dname,e2.sal,
decode(s2.grade,1,'一级',2,'二级',3,'三级',4,'四级',5,'五级') as上司工资级别
from emp e1,emp e2,dept d1,deptd2,salgrade s1,salgrade s2
where e1.mgr = e2.empno
and e1.deptno = d1.deptno
and e2.deptno = d2.deptno
and e1.sal between s1.losal and s1.hisal
and e2.sal between s2.losal and s2.hisal;
-------------------------------------------------------------------------------
select * from emp;
select * from dept;
select * from salgrade;