/* SQL语句的历史版本SQL89比较多 SQL92SQL99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sott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 SWHERE E.DEPTNO = D.DEPTNOAND 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;--右外连接SELECT D.DEPTNO,D.DNAME,E.ENAME FROM EMP E,DEPT D WHERE E.DEPTNO(+) = D.DEPTNO;--左外连接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 MWHERE 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) TWHERE E.SAL>T.ASLAND 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OkALL:必须所有得都满足条件SOME:满足一部分即可*/
