oracle笔记2-多表查询和子查询

--查询出当前用户下的所有表

select table_name from user_tables;

--执行顺序原则：  from  where group by  having   select   order by

--书写顺序原则：  select   from  where  group by  having order by

select * from dept;

select * from emp;

select * from bonus;

select * from salgrade;

--查询出雇员的编号，姓名，部门的编号和名称，地址

select e.empno, e.ename, d.deptno, d.dname, d.loc
   from emp e, dept d
  where e.deptno = d.deptno

--范例：查询出每个员工的上级领导   --自连接  自关联 自查询

--(员工编号、员工姓名、员工部门编号、员工工资、领导编号、领导姓名、领导工资)

select e.empno, e.ename, e.deptno, e.sal, m.empno, m.ename, m.sal
   from emp e, emp m
  where e.mgr = m.empno;

--范例: 查询员工编号、员工姓名、员工部门编号、部门名称,领导编号、领导姓名、领导工资

select e.empno, e.ename, e.deptno, d.dname, m.empno, m.ename, m.sal
   from emp e, emp m, dept d
  where e.mgr = m.empno
    and e.deptno = d.deptno;

--范例：查询出员工编号、员工姓名、员工部门编号、部门名称,员工工资,工资等级,领导编号、领导姓名、领导工资,领导工资等级

--三张表 emp e/m, dept d, salgrade s

select e.empno,
        e.ename,
        e.deptno,
        d.dname,
        e.sal,
        s.grade,
        m.empno,
        m.ename,
        m.sal,
        a.grade
   from emp e, emp m, dept d, salgrade s, salgrade a
  where e.mgr = m.empno
    and e.deptno = d.deptno
    and e.sal between s.losal and s.hisal
    and m.sal between a.losal and a.hisal;

--范例：查询出所有员工的上级领导

--方式一:left join on

select e.empno, e.ename, m.empno, m.ename

from emp e

left join emp m

on e.mgr = m.empno;

--方式二: +

select e.empno, e.ename, m.empno, m.ename

from emp e, emp m

where e.mgr = m.empno(+);

--范例：查询出所有的部门下的员工，要求把没有员工的部门也展示出来

--方式一:left join on

select *

from emp e

right join dept d

on e.deptno = d.deptno

order by e.empno;

--方式二: +

select * from emp e, dept d where e.deptno(+) = d.deptno order by e.empno;

--查询比SCOTT工资高的员工

select * from emp where emp.sal >= (select e.sal from emp e where e.ename = 'SCOTT');--自己也查出来了???

--查询职位是经理并且工资比7782号员工高的员工

select *
   from emp
  where job = 'MANAGER'
    and sal > (select sal from emp e where e.empno = '7782');

--查询工资最低的员工

select * from emp where sal = (select min(e.sal) from emp e);

--查询部门最低工资 大于 30号部门最低工资 的部门

select deptno, min(sal)
   from emp
  group by deptno

having min(sal) > (select min(sal) from emp where deptno = 30)

--查询出和scott同部门并且同职位的员工

select * from emp where deptno = (select deptno from emp where ename = 'SCOTT') and

job = (select job from emp where ename = 'SCOTT');

SELECT * FROM emp WHERE (deptno,job) = (SELECT deptno, job FROM emp WHERE ename = 'SCOTT');

--查询每个部门的最低工资 和最低工资的雇员和部门名称

SELECT e.*,d.dname

FROM emp e, dept d,

(SELECT deptno, MIN(sal) minsal FROM emp GROUP BY deptno) t

WHERE e.sal = t.minsal AND
    e.deptno = d.deptno AND
    e.deptno = t.deptno

--查询出不是领导的员工

SELECT *
   FROM EMP
  WHERE EMPNO NOT IN (SELECT DISTINCT MGR FROM EMP WHERE MGR IS NOT NULL)

--查询员工表中工资最高的前三名

SELECT T.*, ROWNUM
   FROM (SELECT * FROM EMP ORDER BY SAL DESC) T
  WHERE ROWNUM <= 3;

--找到员工表中薪水大于本部门平均薪水的员工

SELECT *
   FROM EMP E,
        (SELECT ROUND(AVG(SAL)) AVGSAL, DEPTNO FROM EMP GROUP BY DEPTNO) T
  WHERE E.DEPTNO = T.DEPTNO
    AND E.SAL > T.AVGSAL
  ORDER BY E.DEPTNO DESC;

--统计每年入职的员工个数

SELECT count(*) counts, to_char(hiredate,'yyyy') years FROM emp GROUP BY to_char(hiredate,'yyyy')

--行转列

SELECT  SUM(counts) "Total",
         SUM(decode(years,'1980',counts)) "1980",
         SUM(DECODE(years,'1981',counts)) "1981",
         SUM(DECODE(years,'1982',counts)) "1982",
         SUM(DECODE(years,'1987',counts)) "1987"

FROM (SELECT count(*) counts, to_char(hiredate,'yyyy') years FROM emp GROUP BY to_char(hiredate,'yyyy'))

--范例：工资大于1500，或者是20号部门下的员工

SELECT * FROM emp WHERE sal > 1500 OR deptno = 20;

--范例：工资大于1500，并且是20号部门下的员工

SELECT * FROM emp WHERE sal > 1500 AND deptno = 20;

--范例：1981年入职的普通员工（不包括总裁和经理）

SELECT * FROM emp WHERE to_char(hiredate,'yyyy') = 1981 AND job NOT IN ('MANAGER','PRESIDENT');

--查询没有员工的部门

SELECT * FROM dept d WHERE NOT  EXISTS (SELECT * FROM emp e WHERE e.deptno = d.deptno );