Oracle - 查询语句 - 多表关联查询

Posted 2020-09-20 路迢迢

/*    
    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 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;
--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 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
*/