✨✨ 欢迎大家来到小伞的大讲堂✨✨养成好习惯先赞后看哦~所属专栏MySQL小伞的主页xiaosan_bloggitee:许星让 (xu-xingrang) - Gitee.com制作不易点个赞吧谢谢喵mysql select * from emp; -------------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------------- | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | | 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | | 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | | 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | | 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | | 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | | 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | | 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | -------------------------------------------------------------------------------- 14 rows in set (0.00 sec)7.1 基本查询查询工资高于500或岗位为MANAGER的雇员同时还要满足他们的姓名首字母为大写的Jmysql select * from emp where (sal 500 or job MANAGER) and ename like J%; -------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------- | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | --------------------------------------------------------------------------按照部门号升序而雇员的工资降序排序mysql select * from emp order by empno asc , sal desc; -------------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------------- | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | | 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | | 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | | 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | | 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | | 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | | 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | | 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | --------------------------------------------------------------------------------使用年薪进行降序排序mysql select ename , sal*12ifnull(comm,0) 年薪 from emp order by 年薪 desc ; ------------------ | ename | 年薪 | ------------------ | KING | 60000.00 | | SCOTT | 36000.00 | | FORD | 36000.00 | | JONES | 35700.00 | | BLAKE | 34200.00 | | CLARK | 29400.00 | | ALLEN | 19500.00 | | TURNER | 18000.00 | | MARTIN | 16400.00 | | MILLER | 15600.00 | | WARD | 15500.00 | | ADAMS | 13200.00 | | JAMES | 11400.00 | | SMITH | 9600.00 | ------------------ 14 rows in set (0.00 sec)显示工资高于平均工资的员工信息mysql select ename , job from emp where sal (select max(sal) from emp); ------------------ | ename | job | ------------------ | KING | PRESIDENT | ------------------ 1 row in set (0.00 sec)显示每个部门的平均工资和最高工资mysql select deptno , format(avg(sal),2) , max(sal) from emp group by deptno; -------------------------------------- | deptno | format(avg(sal),2) | max(sal) | -------------------------------------- | 10 | 2,916.67 | 5000.00 | | 20 | 2,175.00 | 3000.00 | | 30 | 1,566.67 | 2850.00 | -------------------------------------- 3 rows in set (0.00 sec)显示平均工资低于2000的部门号和它的平均工资mysql select deptno , avg(sal) avg_sal from emp group by deptno having avg_sal 2000; --------------------- | deptno | avg_sal | --------------------- | 30 | 1566.666667 | --------------------- 1 row in set (0.00 sec)显示每种岗位的雇员总数平均工资mysql select job , count(*) ,format(avg(sal),2) from emp group by job; ----------------------------------------- | job | count(*) | format(avg(sal),2) | ----------------------------------------- | ANALYST | 2 | 3,000.00 | | CLERK | 4 | 1,037.50 | | MANAGER | 3 | 2,758.33 | | PRESIDENT | 1 | 5,000.00 | | SALESMAN | 4 | 1,400.00 | ----------------------------------------- 5 rows in set (0.00 sec)7.2 多表查询实际开发中往往数据来自不同的表所以需要多表查询。本节我们用一个简单的公司管理系统有三张表EMP,DEPT,SALGRADE来演示如何进行多表查询。显示雇员名、雇员工资以及所在部门的名字因为上面的数据来自EMP和DEPT表因此要联合查询其实我们只要emp表中的deptno dept表中的deptno字段的记录mysql select emp.ename, emp.sal, dept.dname from emp , dept where emp.deptno dept.deptno; ----------------------------- | ename | sal | dname | ----------------------------- | SMITH | 800.00 | RESEARCH | | ALLEN | 1600.00 | SALES | | WARD | 1250.00 | SALES | | JONES | 2975.00 | RESEARCH | | MARTIN | 1250.00 | SALES | | BLAKE | 2850.00 | SALES | | CLARK | 2450.00 | ACCOUNTING | | SCOTT | 3000.00 | RESEARCH | | KING | 5000.00 | ACCOUNTING | | TURNER | 1500.00 | SALES | | ADAMS | 1100.00 | RESEARCH | | JAMES | 950.00 | SALES | | FORD | 3000.00 | RESEARCH | | MILLER | 1300.00 | ACCOUNTING | ----------------------------- 14 rows in set (0.00 sec)显示部门号为10的部门名员工名和工资mysql select ename, sal, dname from emp, dept where emp.deptno dept.deptno and emp.deptno 10; ----------------------------- | ename | sal | dname | ----------------------------- | CLARK | 2450.00 | ACCOUNTING | | KING | 5000.00 | ACCOUNTING | | MILLER | 1300.00 | ACCOUNTING | ----------------------------- 3 rows in set (0.00 sec)显示各个员工的姓名工资及工资级别mysql select ename, sal, grade from emp, salgrade where emp.sal between loosal and hisal; ------------------------ | ename | sal | grade | ------------------------ | SMITH | 800.00 | 1 | | ALLEN | 1600.00 | 3 | | WARD | 1250.00 | 2 | | JONES | 2975.00 | 4 | | MARTIN | 1250.00 | 2 | | BLAKE | 2850.00 | 4 | | CLARK | 2450.00 | 4 | | SCOTT | 3000.00 | 4 | | KING | 5000.00 | 5 | | TURNER | 1500.00 | 3 | | ADAMS | 1100.00 | 1 | | JAMES | 950.00 | 1 | | FORD | 3000.00 | 4 | | MILLER | 1300.00 | 2 | ------------------------ 14 rows in set (0.00 sec)7.3 自连接自连接是指在同一张表连接查询显示员工FORD的上级领导的编号和姓名mgr是员工领导的编号--empno使用子查询mysql select empno, ename from emp where emp.empno(select mgr from emp where ename FORD); --------------- | empno | ename | --------------- | 007566 | JONES | --------------- 1 row in set (0.00 sec)使用多表查询(自查询)-- 使用到表的别名 --from emp leader, emp worker给自己的表起别名因为要先做笛卡尔积所以别名可以先识 别 mysql select leader.empno,leader.ename from emp leader, emp worker whereleader.empno worker.mgr and worker.enameFORD; --------------- | empno | ename | --------------- | 007566 | JONES | --------------- 1 row in set (0.00 sec)7.4 子查询子查询是指嵌入在其他sql语句中的select语句也叫嵌套查询7.4.1 单行子查询返回一行记录的子查询显示SMITH同一部门的员工mysql select * from emp where deptno (select deptno from emp where enameesmith); -------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------- | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | -------------------------------------------------------------------------- 5 rows in set (0.00 sec)7.4.2 多行子查询返回多行记录的子查询in关键字查询和10号部门的工作岗位相同的雇员的名字岗位工资部门号但是不包含10自己的mysql select ename,job,sal,deptno from emp where job in (select distinct job from emp where deptno10) and deptno10; --------------------------------- | ename | job | sal | deptno | --------------------------------- | JONES | MANAGER | 2975.00 | 20 | | BLAKE | MANAGER | 2850.00 | 30 | | SMITH | CLERK | 800.00 | 20 | | ADAMS | CLERK | 1100.00 | 20 | | JAMES | CLERK | 950.00 | 30 | --------------------------------- 5 rows in set (0.00 sec)all关键字显示工资比部门30的所有员工的工资高的员工的姓名、工资和部门号mysql select ename, sal, deptno from emp where sal all(select sal from emp where deptno30); ------------------------ | ename | sal | deptno | ------------------------ | JONES | 2975.00 | 20 | | SCOTT | 3000.00 | 20 | | KING | 5000.00 | 10 | | FORD | 3000.00 | 20 | ------------------------ 4 rows in set (0.00 sec)any关键字显示工资比部门30的任意员工的工资高的员工的姓名、工资和部门号包含自己部门的员工mysql select ename, sal, deptno from emp where sal any(select sal fromemp where deptno30); ------------------------- | ename | sal | deptno | ------------------------- | ALLEN | 1600.00 | 30 | | WARD | 1250.00 | 30 | | JONES | 2975.00 | 20 | | MARTIN | 1250.00 | 30 | | BLAKE | 2850.00 | 30 | | CLARK | 2450.00 | 10 | | SCOTT | 3000.00 | 20 | | KING | 5000.00 | 10 | | TURNER | 1500.00 | 30 | | ADAMS | 1100.00 | 20 | | FORD | 3000.00 | 20 | | MILLER | 1300.00 | 10 | ------------------------- 12 rows in set (0.00 sec)7.4.3 多列子查询单行子查询是指子查询只返回单列单行数据多行子查询是指返回单列多行数据都是针对单列而言的而多列子查询则是指查询返回多个列数据的子查询语句案例查询和SMITH的部门和岗位完全相同的所有雇员不含SMITH本人mysql select ename from emp where (deptno, job)(select deptno, job fromemp where enameSMITH) and ename SMITH; ------- | ename | ------- | ADAMS | ------- 1 row in set (0.00 sec)7.4.4 在from子句中使用子查询子查询语句出现在from子句中。这里要用到数据查询的技巧把一个子查询当做一个临时表使用。案例显示每个高于自己部门平均工资的员工的姓名、部门、工资、平均工资mysql select ename, deptno, sal, format(asal,2) from emp, (select avg(sal)) asal, deptno dt from emp group by deptno) tmp where emp.sal tmp.asal annd emp.deptnotmp.dt; ---------------------------------------- | ename | deptno | sal | format(asal,2) | ---------------------------------------- | KING | 10 | 5000.00 | 2,916.67 | | JONES | 20 | 2975.00 | 2,175.00 | | SCOTT | 20 | 3000.00 | 2,175.00 | | FORD | 20 | 3000.00 | 2,175.00 | | ALLEN | 30 | 1600.00 | 1,566.67 | | BLAKE | 30 | 2850.00 | 1,566.67 | ---------------------------------------- 6 rows in set (0.01 sec)查找每个部门工资最高的人的姓名、工资、部门、最高工资mysql select emp.ename, emp.sal, emp.deptno, ms from emp, - (select max(sal) ms, deptno from emp group by deptno) tmp - where emp.deptnotmp.deptno and emp.saltmp.ms; --------------------------------- | ename | sal | deptno | ms | --------------------------------- | BLAKE | 2850.00 | 30 | 2850.00 | | SCOTT | 3000.00 | 20 | 3000.00 | | KING | 5000.00 | 10 | 5000.00 | | FORD | 3000.00 | 20 | 3000.00 | --------------------------------- 4 rows in set (0.00 sec)显示每个部门的信息部门名编号地址和人员数量方法1使用多表mysql select dept.dname, dept.deptno, dept.loc,count(*) 部门人数 from emp, dept where emp.deptnodept.deptno group by dept.deptno,dept.dname,dept..loc; -------------------------------------------- | dname | deptno | loc | 部门人数 | -------------------------------------------- | ACCOUNTING | 10 | NEW YORK | 3 | | RESEARCH | 20 | DALLAS | 5 | | SALES | 30 | CHICAGO | 6 | -------------------------------------------- 3 rows in set (0.00 sec)方法2使用子查询-- 1. 对EMP表进行人员统计 mysql select count(*), deptno from emp group by deptno; ------------------ | count(*) | deptno | ------------------ | 3 | 10 | | 5 | 20 | | 6 | 30 | ------------------ 3 rows in set (0.00 sec) -- 2. 将上面的表看作临时表 mysql select dept.deptno, dname, mycnt, loc from dept, - (select count(*) mycnt, deptno from emp group by deptno) tmp - where dept.deptnotmp.deptno; ------------------------------------- | deptno | dname | mycnt | loc | ------------------------------------- | 10 | ACCOUNTING | 3 | NEW YORK | | 20 | RESEARCH | 5 | DALLAS | | 30 | SALES | 6 | CHICAGO | ------------------------------------- 3 rows in set (0.00 sec)7.4.5 合并查询在实际应用中为了合并多个select的执行结果可以使用集合操作符 unionunion all7.4.5.1 union该操作符用于取得两个结果集的并集。当使用该操作符时会自动去掉结果集中的重复行。案例将工资大于2500或职位是MANAGER的人找出来mysql select ename, sal, job from emp where sal2500 union - select ename, sal, job from emp where jobMANAGER; --------------------------- | ename | sal | job | --------------------------- | JONES | 2975.00 | MANAGER | | BLAKE | 2850.00 | MANAGER | | SCOTT | 3000.00 | ANALYST | | KING | 5000.00 | PRESIDENT | | FORD | 3000.00 | ANALYST | | CLARK | 2450.00 | MANAGER | --------------------------- 6 rows in set (0.00 sec)7.4.5.2 union all该操作符用于取得两个结果集的并集。当使用该操作符时不会去掉结果集中的重复行。案例将工资大于25000或职位是MANAGER的人找出来mysql select ename, sal, job from emp where sal2500 union all - select ename, sal, job from emp where jobMANAGER; --------------------------- | ename | sal | job | --------------------------- | JONES | 2975.00 | MANAGER | | BLAKE | 2850.00 | MANAGER | | SCOTT | 3000.00 | ANALYST | | KING | 5000.00 | PRESIDENT | | FORD | 3000.00 | ANALYST | | JONES | 2975.00 | MANAGER | | BLAKE | 2850.00 | MANAGER | | CLARK | 2450.00 | MANAGER | --------------------------- 8 rows in set (0.00 sec)
7-MySQL_复合查询
发布时间：2026/6/22 17:28:59
✨✨ 欢迎大家来到小伞的大讲堂✨✨养成好习惯先赞后看哦~所属专栏MySQL小伞的主页xiaosan_bloggitee:许星让 (xu-xingrang) - Gitee.com制作不易点个赞吧谢谢喵mysql select * from emp; -------------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------------- | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | | 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | | 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | | 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | | 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | | 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | | 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | | 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | -------------------------------------------------------------------------------- 14 rows in set (0.00 sec)7.1 基本查询查询工资高于500或岗位为MANAGER的雇员同时还要满足他们的姓名首字母为大写的Jmysql select * from emp where (sal 500 or job MANAGER) and ename like J%; -------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------- | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | --------------------------------------------------------------------------按照部门号升序而雇员的工资降序排序mysql select * from emp order by empno asc , sal desc; -------------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------------- | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | | 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | | 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | | 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | | 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | | 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | | 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | | 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | --------------------------------------------------------------------------------使用年薪进行降序排序mysql select ename , sal*12ifnull(comm,0) 年薪 from emp order by 年薪 desc ; ------------------ | ename | 年薪 | ------------------ | KING | 60000.00 | | SCOTT | 36000.00 | | FORD | 36000.00 | | JONES | 35700.00 | | BLAKE | 34200.00 | | CLARK | 29400.00 | | ALLEN | 19500.00 | | TURNER | 18000.00 | | MARTIN | 16400.00 | | MILLER | 15600.00 | | WARD | 15500.00 | | ADAMS | 13200.00 | | JAMES | 11400.00 | | SMITH | 9600.00 | ------------------ 14 rows in set (0.00 sec)显示工资高于平均工资的员工信息mysql select ename , job from emp where sal (select max(sal) from emp); ------------------ | ename | job | ------------------ | KING | PRESIDENT | ------------------ 1 row in set (0.00 sec)显示每个部门的平均工资和最高工资mysql select deptno , format(avg(sal),2) , max(sal) from emp group by deptno; -------------------------------------- | deptno | format(avg(sal),2) | max(sal) | -------------------------------------- | 10 | 2,916.67 | 5000.00 | | 20 | 2,175.00 | 3000.00 | | 30 | 1,566.67 | 2850.00 | -------------------------------------- 3 rows in set (0.00 sec)显示平均工资低于2000的部门号和它的平均工资mysql select deptno , avg(sal) avg_sal from emp group by deptno having avg_sal 2000; --------------------- | deptno | avg_sal | --------------------- | 30 | 1566.666667 | --------------------- 1 row in set (0.00 sec)显示每种岗位的雇员总数平均工资mysql select job , count(*) ,format(avg(sal),2) from emp group by job; ----------------------------------------- | job | count(*) | format(avg(sal),2) | ----------------------------------------- | ANALYST | 2 | 3,000.00 | | CLERK | 4 | 1,037.50 | | MANAGER | 3 | 2,758.33 | | PRESIDENT | 1 | 5,000.00 | | SALESMAN | 4 | 1,400.00 | ----------------------------------------- 5 rows in set (0.00 sec)7.2 多表查询实际开发中往往数据来自不同的表所以需要多表查询。本节我们用一个简单的公司管理系统有三张表EMP,DEPT,SALGRADE来演示如何进行多表查询。显示雇员名、雇员工资以及所在部门的名字因为上面的数据来自EMP和DEPT表因此要联合查询其实我们只要emp表中的deptno dept表中的deptno字段的记录mysql select emp.ename, emp.sal, dept.dname from emp , dept where emp.deptno dept.deptno; ----------------------------- | ename | sal | dname | ----------------------------- | SMITH | 800.00 | RESEARCH | | ALLEN | 1600.00 | SALES | | WARD | 1250.00 | SALES | | JONES | 2975.00 | RESEARCH | | MARTIN | 1250.00 | SALES | | BLAKE | 2850.00 | SALES | | CLARK | 2450.00 | ACCOUNTING | | SCOTT | 3000.00 | RESEARCH | | KING | 5000.00 | ACCOUNTING | | TURNER | 1500.00 | SALES | | ADAMS | 1100.00 | RESEARCH | | JAMES | 950.00 | SALES | | FORD | 3000.00 | RESEARCH | | MILLER | 1300.00 | ACCOUNTING | ----------------------------- 14 rows in set (0.00 sec)显示部门号为10的部门名员工名和工资mysql select ename, sal, dname from emp, dept where emp.deptno dept.deptno and emp.deptno 10; ----------------------------- | ename | sal | dname | ----------------------------- | CLARK | 2450.00 | ACCOUNTING | | KING | 5000.00 | ACCOUNTING | | MILLER | 1300.00 | ACCOUNTING | ----------------------------- 3 rows in set (0.00 sec)显示各个员工的姓名工资及工资级别mysql select ename, sal, grade from emp, salgrade where emp.sal between loosal and hisal; ------------------------ | ename | sal | grade | ------------------------ | SMITH | 800.00 | 1 | | ALLEN | 1600.00 | 3 | | WARD | 1250.00 | 2 | | JONES | 2975.00 | 4 | | MARTIN | 1250.00 | 2 | | BLAKE | 2850.00 | 4 | | CLARK | 2450.00 | 4 | | SCOTT | 3000.00 | 4 | | KING | 5000.00 | 5 | | TURNER | 1500.00 | 3 | | ADAMS | 1100.00 | 1 | | JAMES | 950.00 | 1 | | FORD | 3000.00 | 4 | | MILLER | 1300.00 | 2 | ------------------------ 14 rows in set (0.00 sec)7.3 自连接自连接是指在同一张表连接查询显示员工FORD的上级领导的编号和姓名mgr是员工领导的编号--empno使用子查询mysql select empno, ename from emp where emp.empno(select mgr from emp where ename FORD); --------------- | empno | ename | --------------- | 007566 | JONES | --------------- 1 row in set (0.00 sec)使用多表查询(自查询)-- 使用到表的别名 --from emp leader, emp worker给自己的表起别名因为要先做笛卡尔积所以别名可以先识 别 mysql select leader.empno,leader.ename from emp leader, emp worker whereleader.empno worker.mgr and worker.enameFORD; --------------- | empno | ename | --------------- | 007566 | JONES | --------------- 1 row in set (0.00 sec)7.4 子查询子查询是指嵌入在其他sql语句中的select语句也叫嵌套查询7.4.1 单行子查询返回一行记录的子查询显示SMITH同一部门的员工mysql select * from emp where deptno (select deptno from emp where enameesmith); -------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------- | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | -------------------------------------------------------------------------- 5 rows in set (0.00 sec)7.4.2 多行子查询返回多行记录的子查询in关键字查询和10号部门的工作岗位相同的雇员的名字岗位工资部门号但是不包含10自己的mysql select ename,job,sal,deptno from emp where job in (select distinct job from emp where deptno10) and deptno10; --------------------------------- | ename | job | sal | deptno | --------------------------------- | JONES | MANAGER | 2975.00 | 20 | | BLAKE | MANAGER | 2850.00 | 30 | | SMITH | CLERK | 800.00 | 20 | | ADAMS | CLERK | 1100.00 | 20 | | JAMES | CLERK | 950.00 | 30 | --------------------------------- 5 rows in set (0.00 sec)all关键字显示工资比部门30的所有员工的工资高的员工的姓名、工资和部门号mysql select ename, sal, deptno from emp where sal all(select sal from emp where deptno30); ------------------------ | ename | sal | deptno | ------------------------ | JONES | 2975.00 | 20 | | SCOTT | 3000.00 | 20 | | KING | 5000.00 | 10 | | FORD | 3000.00 | 20 | ------------------------ 4 rows in set (0.00 sec)any关键字显示工资比部门30的任意员工的工资高的员工的姓名、工资和部门号包含自己部门的员工mysql select ename, sal, deptno from emp where sal any(select sal fromemp where deptno30); ------------------------- | ename | sal | deptno | ------------------------- | ALLEN | 1600.00 | 30 | | WARD | 1250.00 | 30 | | JONES | 2975.00 | 20 | | MARTIN | 1250.00 | 30 | | BLAKE | 2850.00 | 30 | | CLARK | 2450.00 | 10 | | SCOTT | 3000.00 | 20 | | KING | 5000.00 | 10 | | TURNER | 1500.00 | 30 | | ADAMS | 1100.00 | 20 | | FORD | 3000.00 | 20 | | MILLER | 1300.00 | 10 | ------------------------- 12 rows in set (0.00 sec)7.4.3 多列子查询单行子查询是指子查询只返回单列单行数据多行子查询是指返回单列多行数据都是针对单列而言的而多列子查询则是指查询返回多个列数据的子查询语句案例查询和SMITH的部门和岗位完全相同的所有雇员不含SMITH本人mysql select ename from emp where (deptno, job)(select deptno, job fromemp where enameSMITH) and ename SMITH; ------- | ename | ------- | ADAMS | ------- 1 row in set (0.00 sec)7.4.4 在from子句中使用子查询子查询语句出现在from子句中。这里要用到数据查询的技巧把一个子查询当做一个临时表使用。案例显示每个高于自己部门平均工资的员工的姓名、部门、工资、平均工资mysql select ename, deptno, sal, format(asal,2) from emp, (select avg(sal)) asal, deptno dt from emp group by deptno) tmp where emp.sal tmp.asal annd emp.deptnotmp.dt; ---------------------------------------- | ename | deptno | sal | format(asal,2) | ---------------------------------------- | KING | 10 | 5000.00 | 2,916.67 | | JONES | 20 | 2975.00 | 2,175.00 | | SCOTT | 20 | 3000.00 | 2,175.00 | | FORD | 20 | 3000.00 | 2,175.00 | | ALLEN | 30 | 1600.00 | 1,566.67 | | BLAKE | 30 | 2850.00 | 1,566.67 | ---------------------------------------- 6 rows in set (0.01 sec)查找每个部门工资最高的人的姓名、工资、部门、最高工资mysql select emp.ename, emp.sal, emp.deptno, ms from emp, - (select max(sal) ms, deptno from emp group by deptno) tmp - where emp.deptnotmp.deptno and emp.saltmp.ms; --------------------------------- | ename | sal | deptno | ms | --------------------------------- | BLAKE | 2850.00 | 30 | 2850.00 | | SCOTT | 3000.00 | 20 | 3000.00 | | KING | 5000.00 | 10 | 5000.00 | | FORD | 3000.00 | 20 | 3000.00 | --------------------------------- 4 rows in set (0.00 sec)显示每个部门的信息部门名编号地址和人员数量方法1使用多表mysql select dept.dname, dept.deptno, dept.loc,count(*) 部门人数 from emp, dept where emp.deptnodept.deptno group by dept.deptno,dept.dname,dept..loc; -------------------------------------------- | dname | deptno | loc | 部门人数 | -------------------------------------------- | ACCOUNTING | 10 | NEW YORK | 3 | | RESEARCH | 20 | DALLAS | 5 | | SALES | 30 | CHICAGO | 6 | -------------------------------------------- 3 rows in set (0.00 sec)方法2使用子查询-- 1. 对EMP表进行人员统计 mysql select count(*), deptno from emp group by deptno; ------------------ | count(*) | deptno | ------------------ | 3 | 10 | | 5 | 20 | | 6 | 30 | ------------------ 3 rows in set (0.00 sec) -- 2. 将上面的表看作临时表 mysql select dept.deptno, dname, mycnt, loc from dept, - (select count(*) mycnt, deptno from emp group by deptno) tmp - where dept.deptnotmp.deptno; ------------------------------------- | deptno | dname | mycnt | loc | ------------------------------------- | 10 | ACCOUNTING | 3 | NEW YORK | | 20 | RESEARCH | 5 | DALLAS | | 30 | SALES | 6 | CHICAGO | ------------------------------------- 3 rows in set (0.00 sec)7.4.5 合并查询在实际应用中为了合并多个select的执行结果可以使用集合操作符 unionunion all7.4.5.1 union该操作符用于取得两个结果集的并集。当使用该操作符时会自动去掉结果集中的重复行。案例将工资大于2500或职位是MANAGER的人找出来mysql select ename, sal, job from emp where sal2500 union - select ename, sal, job from emp where jobMANAGER; --------------------------- | ename | sal | job | --------------------------- | JONES | 2975.00 | MANAGER | | BLAKE | 2850.00 | MANAGER | | SCOTT | 3000.00 | ANALYST | | KING | 5000.00 | PRESIDENT | | FORD | 3000.00 | ANALYST | | CLARK | 2450.00 | MANAGER | --------------------------- 6 rows in set (0.00 sec)7.4.5.2 union all该操作符用于取得两个结果集的并集。当使用该操作符时不会去掉结果集中的重复行。案例将工资大于25000或职位是MANAGER的人找出来mysql select ename, sal, job from emp where sal2500 union all - select ename, sal, job from emp where jobMANAGER; --------------------------- | ename | sal | job | --------------------------- | JONES | 2975.00 | MANAGER | | BLAKE | 2850.00 | MANAGER | | SCOTT | 3000.00 | ANALYST | | KING | 5000.00 | PRESIDENT | | FORD | 3000.00 | ANALYST | | JONES | 2975.00 | MANAGER | | BLAKE | 2850.00 | MANAGER | | CLARK | 2450.00 | MANAGER | --------------------------- 8 rows in set (0.00 sec)
![如何快速构建AI音视频总结工具：BibiGPT技术架构深度解析 [特殊字符]](http://pic.xiahunao.cn/yaotu/如何快速构建AI音视频总结工具：BibiGPT技术架构深度解析 [特殊字符])
