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查询的员工部门表结构#xff1a;
mysql show tables;
-----------------
| Tables_in_scott |
-----------------
| dept …
文章目录基本查询回顾多表查询自连接子查询单行子查询多行子查询多列子查询在from子句中使用子查询合并查询unionunion all基本查询回顾
查询的员工部门表结构
mysql show tables;
-----------------
| Tables_in_scott |
-----------------
| dept |
| emp |
| salgrade |
-----------------
3 rows in set (0.00 sec)mysql desc dept;
-------------------------------------------------------------
| Field | Type | Null | Key | Default | Extra |
-------------------------------------------------------------
| deptno | int(2) unsigned zerofill | NO | | NULL | |
| dname | varchar(14) | YES | | NULL | |
| loc | varchar(13) | YES | | NULL | |
-------------------------------------------------------------
3 rows in set (0.00 sec)mysql desc emp;
---------------------------------------------------------------
| Field | Type | Null | Key | Default | Extra |
---------------------------------------------------------------
| empno | int(6) unsigned zerofill | NO | | NULL | |
| ename | varchar(10) | YES | | NULL | |
| job | varchar(9) | YES | | NULL | |
| mgr | int(4) unsigned zerofill | YES | | NULL | |
| hiredate | datetime | YES | | NULL | |
| sal | decimal(7,2) | YES | | NULL | |
| comm | decimal(7,2) | YES | | NULL | |
| deptno | int(2) unsigned zerofill | YES | | NULL | |
---------------------------------------------------------------
8 rows in set (0.00 sec)mysql desc salgrade;
-------------------------------------------
| Field | Type | Null | Key | Default | Extra |
-------------------------------------------
| grade | int(11) | YES | | NULL | |
| losal | int(11) | YES | | NULL | |
| hisal | int(11) | YES | | NULL | |
-------------------------------------------
3 rows in set (0.00 sec)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J
mysql select job, ename, sal from emp where (sal500 or jobMANAGER) and ename like J%;
-------------------------
| job | ename | sal |
-------------------------
| MANAGER | JONES | 2975.00 |
| CLERK | JAMES | 950.00 |
-------------------------
2 rows in set (0.00 sec)按照部门号升序而雇员的工资降序排序
mysql select ename, sal, deptno from emp order by deptno asc, sal desc;
-------------------------
| ename | sal | deptno |
-------------------------
| KING | 5000.00 | 10 |
| CLARK | 2450.00 | 10 |
| MILLER | 1300.00 | 10 |
| SCOTT | 3000.00 | 20 |
| FORD | 3000.00 | 20 |
| JONES | 2975.00 | 20 |
| ADAMS | 1100.00 | 20 |
| SMITH | 800.00 | 20 |
| BLAKE | 2850.00 | 30 |
| ALLEN | 1600.00 | 30 |
| TURNER | 1500.00 | 30 |
| WARD | 1250.00 | 30 |
| MARTIN | 1250.00 | 30 |
| JAMES | 950.00 | 30 |
-------------------------
14 rows in set (0.00 sec)使用年薪进行降序排序
mysql select ename, sal*12ifnull(comm,0) year_sal from emp order by year_sal desc;
------------------
| ename | year_sal |
------------------
| 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)显示工资最高的员工的名字和工作岗位
mysql select ename, job from emp where sal(select max(sal) from emp);
------------------
| ename | job |
------------------
| KING | PRESIDENT |
------------------
1 row in set (0.00 sec)显示工资高于平均工资的员工信息
mysql select ename, sal from emp where sal(select avg(sal) from emp);
----------------
| ename | sal |
----------------
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| SCOTT | 3000.00 |
| KING | 5000.00 |
| FORD | 3000.00 |
----------------
6 rows in set (0.00 sec)显示每个部门的平均工资和最高工资
mysql select deptno, max(sal), avg(sal) from emp group by deptno;
-------------------------------
| deptno | max(sal) | avg(sal) |
-------------------------------
| 10 | 5000.00 | 2916.666667 |
| 20 | 3000.00 | 2175.000000 |
| 30 | 2850.00 | 1566.666667 |
-------------------------------
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_sal2000;
---------------------
| 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(*) 雇员总数, avg(sal) 平均工资 from emp group by job;
---------------------------------------
| job | 雇员总数 | 平均工资 |
---------------------------------------
| ANALYST | 2 | 3000.000000 |
| CLERK | 4 | 1037.500000 |
| MANAGER | 3 | 2758.333333 |
| PRESIDENT | 1 | 5000.000000 |
| SALESMAN | 4 | 1400.000000 |
---------------------------------------
5 rows in set (0.00 sec)多表查询
在实际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
案例
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 mysql select * from emp, dept limit 12;
-----------------------------------------------------------------------------------------------------------
| empno | ename | job | mgr | hiredate | sal | comm | deptno | deptno | dname | loc |
-----------------------------------------------------------------------------------------------------------
| 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | 10 | ACCOUNTING | NEW YORK |
| 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | 20 | RESEARCH | DALLAS |
| 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | 30 | SALES | CHICAGO |
| 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | 40 | OPERATIONS | BOSTON |
| 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | 10 | ACCOUNTING | NEW YORK |
| 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | 20 | RESEARCH | DALLAS |
| 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | 30 | SALES | CHICAGO |
| 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | 40 | OPERATIONS | BOSTON |
| 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | 10 | ACCOUNTING | NEW YORK |
| 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | 20 | RESEARCH | DALLAS |
| 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | 30 | SALES | CHICAGO |
| 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | 40 | OPERATIONS | BOSTON |
-----------------------------------------------------------------------------------------------------------
12 rows in set (0.00 sec)此时就需要对表的数据进行筛选只要emp表中的deptno dept表中的deptno字段的记录
mysql select ename, sal, dname from emp, dept where emp.deptnodept.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 emp.deptno, dname, ename, sal from emp, dept where emp.deptnodept.deptno and emp.deptno10;
-------------------------------------
| deptno | dname | ename | sal |
-------------------------------------
| 10 | ACCOUNTING | CLARK | 2450.00 |
| 10 | ACCOUNTING | KING | 5000.00 |
| 10 | ACCOUNTING | MILLER | 1300.00 |
-------------------------------------
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 sal between losal 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)自连接
自连接是指在同一张表连接查询
案例
显示员工FORD的上级领导的编号和姓名
子查询
mysql select empno, ename from emp where empno(select mgr from emp where enameFORD);
---------------
| empno | ename |
---------------
| 007566 | JONES |
---------------
1 row in set (0.00 sec)使用多表查询自查询
mysql select leader.empno, leader.ename from emp leader,emp worker where worker.mgrleader.empno and worker.enameFORD;
---------------
| empno | ename |
---------------
| 007566 | JONES |
---------------
1 row in set (0.00 sec)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
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 ename, job from emp where job(select job from emp where enameSMITH);
---------------
| ename | job |
---------------
| SMITH | CLERK |
| ADAMS | CLERK |
| JAMES | CLERK |
| MILLER | CLERK |
---------------
4 rows in set (0.00 sec)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号部门
mysql select ename, job, sal, deptno from emp where job in(select job from emp where deptno10);
------------------------------------
| ename | job | sal | deptno |
------------------------------------
| JONES | MANAGER | 2975.00 | 20 |
| BLAKE | MANAGER | 2850.00 | 30 |
| CLARK | MANAGER | 2450.00 | 10 |
| KING | PRESIDENT | 5000.00 | 10 |
| SMITH | CLERK | 800.00 | 20 |
| ADAMS | CLERK | 1100.00 | 20 |
| JAMES | CLERK | 950.00 | 30 |
| MILLER | CLERK | 1300.00 | 10 |
------------------------------------
8 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
mysql select ename, sal, deptno from emp where sal any(select sal from emp 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 (0.01 sec)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。
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 from emp where enameSMITH) and ename!SMITH;
-------
| ename |
-------
| ADAMS |
-------
1 row in set (0.00 sec)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。
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, emp.deptno, sal, avg_tb.avg_sal from emp, (select deptno, avg(sal) avg_sal from emp group by deptno) avg_tb where emp.deptnoavg_tb.deptno and emp.salavg_tb.avg_sal;
-------------------------------------
| ename | deptno | sal | avg_sal |
-------------------------------------
| ALLEN | 30 | 1600.00 | 1566.666667 |
| JONES | 20 | 2975.00 | 2175.000000 |
| BLAKE | 30 | 2850.00 | 1566.666667 |
| SCOTT | 20 | 3000.00 | 2175.000000 |
| KING | 10 | 5000.00 | 2916.666667 |
| FORD | 20 | 3000.00 | 2175.000000 |
-------------------------------------
6 rows in set (0.00 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 ename, sal, emp.deptno, max_tb.max_sal from emp, (select deptno, max(sal) max_sal from emp group by deptno) max_tb where emp.deptnomax_tb.deptno and emp.salmax_tb.max_sal;
---------------------------------
| ename | sal | deptno | max_sal |
---------------------------------
| 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
方法一使用多表查询
mysql select dept.dname, emp.deptno, dept.loc, count(*) cnt from emp, dept where emp.deptnodept.deptno group by dept.deptno, dept.loc, dept.dname;
-----------------------------------
| dname | deptno | loc | cnt |
-----------------------------------
| ACCOUNTING | 10 | NEW YORK | 3 |
| RESEARCH | 20 | DALLAS | 5 |
| SALES | 30 | CHICAGO | 6 |
-----------------------------------
3 rows in set (0.00 sec)方法二使用子查询
mysql select dname, dept.deptno, loc, cnt_tb.cnt from dept, (select emp.deptno, count(*) cnt from emp group by deptno) cnt_tb where deept.deptnocnt_tb.deptno;
-----------------------------------
| dname | deptno | loc | cnt |
-----------------------------------
| ACCOUNTING | 10 | NEW YORK | 3 |
| RESEARCH | 20 | DALLAS | 5 |
| SALES | 30 | CHICAGO | 6 |
-----------------------------------
3 rows in set (0.00 sec)合并查询
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。
将工资大于2500或职位是MANAGER的人找出来
mysql select ename, job, sal from emp where sal2500 union select ename, job, sal from emp where jobMANAGER;
---------------------------
| ename | job | sal |
---------------------------
| JONES | MANAGER | 2975.00 |
| BLAKE | MANAGER | 2850.00 |
| SCOTT | ANALYST | 3000.00 |
| KING | PRESIDENT | 5000.00 |
| FORD | ANALYST | 3000.00 |
| CLARK | MANAGER | 2450.00 |
---------------------------
6 rows in set (0.00 sec)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。
将工资大于2500或职位是MANAGER的人找出来
mysql select ename, job, sal from emp where sal2500 union all select ename, job, sal from emp where jobMANAGER;
---------------------------
| ename | job | sal |
---------------------------
| JONES | MANAGER | 2975.00 |
| BLAKE | MANAGER | 2850.00 |
| SCOTT | ANALYST | 3000.00 |
| KING | PRESIDENT | 5000.00 |
| FORD | ANALYST | 3000.00 |
| JONES | MANAGER | 2975.00 |
| BLAKE | MANAGER | 2850.00 |
| CLARK | MANAGER | 2450.00 |
---------------------------
8 rows in set (0.00 sec)
