/*
SQL语句的历史版本
SQL89
比较多
SQL92
SQL99
多表关联查询
笛卡尔积
等值关联查询
非等值关联查询
左外连接
右外连接
全外连接
自连接
*/
----------------------------------92语法
--查询部门名称和员工名称(两张表的关联没有任何的约束条件)
SELECT * FROM EMP;
SELECT * FROM DEPT;
SELECT * FROM SALGRADE;
SELECT * FROM EMP,DEPT;
SELECT * FROM EMP,DEPT,SALGRADE;
--等值关联查询
SELECT * FROM EMP,DEPT WHERE EMP.DEPTNO = DEPT.DEPTNO;
SELECT DEPT.DNAME,EMP.ENAME FROM EMP,DEPT WHERE EMP.DEPTNO = DEPT.DEPTNO;
--查询scott所在的部门名称
SELECT DEPT.DNAME FROM EMP,DEPT WHERE EMP.DEPTNO = DEPT.DEPTNO AND EMP.ENAME = 'SCOTT';
--非等值关联查询
SELECT EMP.ENAME,EMP.SAL,SALGRADE.GRADE FROM EMP,SALGRADE WHERE EMP.SAL BETWEEN SALGRADE.LOSAL AND SALGRADE.HISAL;
--给表设置一个别名，这个别名只有当前查询有效
SELECT E.ENAME,E.SAL,S.GRADE FROM EMP E,SALGRADE S WHERE E.SAL BETWEEN S.LOSAL AND S.HISAL;
--查询部门编号，部门名称，员工姓名，员工薪资，员工薪资等级
SELECT D.DEPTNO,D.DNAME,E.ENAME,E.SAL,S.GRADE FROM EMP E,DEPT D,SALGRADE S
WHERE E.DEPTNO = D.DEPTNO
AND E.SAL BETWEEN S.LOSAL AND S.HISAL;
--外连接:就是为了找回不符合条件的数据
SELECT DEPTNO,COUNT(*) FROM EMP GROUP BY DEPTNO;
SELECT D.DEPTNO,D.DNAME,E.ENAME FROM EMP E,DEPT D WHERE E.DEPTNO = D.DEPTNO;
(注意：一般是哪边可能会少数据就放在哪边，比如员工表里面有些员工可能还没有分部门，所以没有部门编号，所以要外链接的话，加号放在员工表这边)
--左外连接
SELECT D.DEPTNO,D.DNAME,E.ENAME FROM EMP E,DEPT D WHERE E.DEPTNO(+) = D.DEPTNO;
--右外连接
SELECT D.DEPTNO,D.DNAME,E.ENAME FROM EMP E,DEPT D WHERE E.DEPTNO = D.DEPTNO(+);
--修改数据
UPDATE EMP SET DEPTNO = NULL WHERE EMPNO = 7934;
COMMIT;
--自连接
SELECT * FROM EMP;
--查询当前员工和经理的名字
SELECT E.ENAME ,E.MGR ,M.ENAME,M.EMPNO FROM EMP E,EMP M
WHERE E.MGR = M.EMPNO(+);
----------------------------------99语法
--笛卡尔积
SELECT * FROM EMP E,DEPT D;
SELECT * FROM EMP E CROSS JOIN DEPT D;
--等值连接(就是自动匹配名字，类型相同的列)
SELECT * FROM EMP E NATURAL JOIN DEPT D;
SELECT * FROM EMP E JOIN DEPT D USING(DEPTNO);
SELECT * FROM EMP E JOIN DEPT D ON(E.DEPTNO = D.DEPTNO);
--非等值连接
SELECT * FROM EMP E JOIN SALGRADE S ON(E.SAL BETWEEN S.LOSAL AND S.HISAL);
--外连接
SELECT * FROM EMP E LEFT JOIN DEPT D USING(DEPTNO);
SELECT * FROM EMP E RIGHT JOIN DEPT D USING(DEPTNO);
SELECT * FROM EMP E FULL JOIN DEPT D USING(DEPTNO);
--自连接
SELECT E.ENAME,M.ENAME FROM EMP E JOIN EMP M ON(E.MGR = M.EMPNO);
SELECT E.ENAME,M.ENAME FROM EMP E LEFT JOIN EMP M ON(E.MGR = M.EMPNO);
--子查询(作为查询条件)
SELECT * FROM EMP WHERE SAL = (SELECT MAX(SAL) FROM EMP);
SELECT * FROM EMP WHERE SAL > (SELECT AVG(SAL) FROM EMP);
--子查询(作为一张虚拟的表)
SELECT * FROM EMP E ,(SELECT AVG(SAL) ASL,DEPTNO FROM EMP GROUP BY DEPTNO) T
WHERE E.SAL>T.ASL
AND E.DEPTNO = T.DEPTNO;
--单行子查询
SELECT * FROM EMP WHERE SAL = (SELECT MAX(SAL) FROM EMP);
--多行子查询
SELECT * FROM EMP E WHERE E.SAL IN(SELECT MAX(SAL) FROM EMP WHERE DEPTNO IS NOT NULL GROUP BY DEPTNO);
/*
IN:取其中之一相等就Ok
ALL:必须所有得都满足条件
SOME:满足一部分即可
*/