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34个数据库练习题 带你打开思路

------mysql数据库练习题-------
学习基础知识的同时，没有练习题可不行
博主在这里给大家整理了34个数据库练习题
希望能帮助同学们打开思路。

注：使用的语句已用代码块的形式标注出

文章目录

34个数据库练习题带你打开思路

1、取得每个部门最高薪水的人员名称

第一步：取得每个部门最高薪水(按照部门编号分组，找出每一组最大值)

mysql> select deptno,max(sal) as maxsal from emp group by deptno;

±-------±--------+
| deptno | maxsal |
±-------±--------+
| 10 | 5000.00 |
| 20 | 3000.00 |
| 30 | 2850.00 |
±-------±--------+
第二步：将以上的查询结果当做一张临时表t，
t和emp表连接，条件：t.deptno = e.deptno and t.maxsal = e.sal

select 
    e.ename, t.*
from 
    emp e
join
    (select deptno,max(sal) as maxsal from emp group by deptno) t
on
    t.deptno = e.deptno and t.maxsal = e.sal;

±------±-------±--------+
| ename | deptno | maxsal |
±------±-------±--------+
| BLAKE | 30 | 2850.00 |
| SCOTT | 20 | 3000.00 |
| KING | 10 | 5000.00 |
| FORD | 20 | 3000.00 |
±------±-------±--------+

2、哪些人的薪水在部门的平均薪水之上

第一步：找出每个部门的平均薪水

select deptno,avg(sal) as avgsal from emp group by deptno;

±-------±------------+
| deptno | avgsal |
±-------±------------+
| 10 | 2916.666667 |
| 20 | 2175.000000 |
| 30 | 1566.666667 |
±-------±------------+
第二步：将以上查询结果当做t表，t和emp表连接
条件：部门编号相同，并且emp的sal大于t表的avgsal

select 
    t.*, e.ename, e.sal
from
    emp e
join
    (select deptno,avg(sal) as avgsal from emp group by deptno) t
on
    e.deptno = t.deptno and e.sal > t.avgsal;

±-------±------------±------±--------+
| deptno | avgsal | ename | sal |
±-------±------------±------±--------+
| 30 | 1566.666667 | ALLEN | 1600.00 |
| 20 | 2175.000000 | JONES | 2975.00 |
| 30 | 1566.666667 | BLAKE | 2850.00 |
| 20 | 2175.000000 | SCOTT | 3000.00 |
| 10 | 2916.666667 | KING | 5000.00 |
| 20 | 2175.000000 | FORD | 3000.00 |
±-------±------------±------±--------+

3、取得部门中（所有人的）平均的薪水等级

平均的薪水等级：先计算每一个薪水的等级，然后找出薪水等级的平均值。

平均薪水的等级：先计算平均薪水，然后找出每个平均薪水的等级值。

第一步：找出每个人的薪水等级
emp e和salgrade s表连接。
连接条件：e.sal between s.losal and s.hisal

select 
    e.ename,e.sal,e.deptno,s.grade
from
    emp e
join
    salgrade s
on
    e.sal between s.losal and s.hisal;

±-------±--------±-------±------+
| ename | sal | deptno | grade |
±-------±--------±-------±------+
| CLARK | 2450.00 | 10 | 4 |
| KING | 5000.00 | 10 | 5 |
| MILLER | 1300.00 | 10 | 2 |

| SMITH | 800.00 | 20 | 1 |
| ADAMS | 1100.00 | 20 | 1 |
| SCOTT | 3000.00 | 20 | 4 |
| FORD | 3000.00 | 20 | 4 |
| JONES | 2975.00 | 20 | 4 |

| MARTIN | 1250.00 | 30 | 2 |
| TURNER | 1500.00 | 30 | 3 |
| BLAKE | 2850.00 | 30 | 4 |
| ALLEN | 1600.00 | 30 | 3 |
| JAMES | 950.00 | 30 | 1 |
| WARD | 1250.00 | 30 | 2 |
±-------±--------±-------±------+

第二步：基于以上的结果继续按照deptno分组，求grade的平均值。

select 
    e.deptno,avg(s.grade)
from
    emp e
join
    salgrade s
on
    e.sal between s.losal and s.hisal
group by
    e.deptno;

±-------±-------------+
| deptno | avg(s.grade) |
±-------±-------------+
| 10 | 3.6667 |
| 20 | 2.8000 |
| 30 | 2.5000 |
±-------±-------------+

4、不准用组函数（Max ），取得最高薪水

第一种：sal降序，limit 1

select ename,sal from emp order by sal desc limit 1;

±------±--------+
| ename | sal |
±------±--------+
| KING | 5000.00 |
±------±--------+

第二种方案：

select max(sal) from emp;

第三种方案：表的自连接

select sal from emp where sal not in(select distinct a.sal from emp a join emp b on a.sal < b.sal);

±--------+
| sal |
±--------+
| 5000.00 |
±--------+

select 
    distinct a.sal 
from 
    emp a 
join 
    emp b 
on 
    a.sal < b.sal

a表
±--------+
| sal |
±--------+
| 800.00 |
| 1600.00 |
| 1250.00 |
| 2975.00 |
| 1250.00 |
| 2850.00 |
| 2450.00 |
| 3000.00 |
| 5000.00 |
| 1500.00 |
| 1100.00 |
| 950.00 |
| 3000.00 |
| 1300.00 |
±--------+

b表
±--------+
| sal |
±--------+
| 800.00 |
| 1600.00 |
| 1250.00 |
| 2975.00 |
| 1250.00 |
| 2850.00 |
| 2450.00 |
| 3000.00 |
| 5000.00 |
| 1500.00 |
| 1100.00 |
| 950.00 |
| 3000.00 |
| 1300.00 |
±--------+

5、取得平均薪水最高的部门的部门编号

第一种方案：降序取第一个。

第一步：找出每个部门的平均薪水

select deptno,avg(sal) as avgsal from emp group by deptno;

±-------±------------+
| deptno | avgsal |
±-------±------------+
| 10 | 2916.666667 |
| 20 | 2175.000000 |
| 30 | 1566.666667 |
±-------±------------+

第二步：降序选第一个。

select deptno,avg(sal) as avgsal from emp group by deptno order by avgsal desc limit 1;

±-------±------------+
| deptno | avgsal |
±-------±------------+
| 10 | 2916.666667 |
±-------±------------+

第二种方案：max

第一步：找出每个部门的平均薪水

select deptno,avg(sal) as avgsal from emp group by deptno;

±-------±------------+
| deptno | avgsal |
±-------±------------+
| 10 | 2916.666667 |
| 20 | 2175.000000 |
| 30 | 1566.666667 |
±-------±------------+

第二步：找出以上结果中avgsal最大的值。

select max(t.avgsal) from (select avg(sal) as avgsal from emp group by deptno) t;

±--------------+
| max(t.avgsal) |
±--------------+
| 2916.666667 |
±--------------+

第三步：

select 
    deptno,avg(sal) as avgsal 
from 
    emp 
group by 
    deptno
having
    avgsal = (select max(t.avgsal) from (select avg(sal) as avgsal from emp group by deptno) t);

±-------±------------+
| deptno | avgsal |
±-------±------------+
| 10 | 2916.666667 |
±-------±------------+

6、取得平均薪水最高的部门的部门名称

select 
    d.dname,avg(e.sal) as avgsal 
from 
    emp e
join
    dept d
on
    e.deptno = d.deptno
group by 
    d.dname
order by 
    avgsal desc 
limit 
    1;

±-----------±------------+
| dname | avgsal |
±-----------±------------+
| ACCOUNTING | 2916.666667 |
±-----------±------------+

7、求平均薪水的等级最低的部门的部门名称

平均薪水是800
平均薪水是900
那么他俩都是1级别。

第一步：找出每个部门的平均薪水

select deptno,avg(sal) as avgsal from emp group by deptno;

±-------±------------+
| deptno | avgsal |
±-------±------------+
| 10 | 2916.666667 |
| 20 | 2175.000000 |
| 30 | 1566.666667 |
±-------±------------+

第二步：找出每个部门的平均薪水的等级
以上t表和salgrade表连接，条件：t.avgsal between s.losal and s.hisal

select 
    t.*,s.grade
from
    (select d.dname,avg(sal) as avgsal from emp e join dept d on e.deptno = d.deptno group by d.dname) t
join
    salgrade s
on
    t.avgsal between s.losal and s.hisal;

±-----------±------------±------+
| dname | avgsal | grade |
±-----------±------------±------+
| SALES | 1566.666667 | 3 |
| ACCOUNTING | 2916.666667 | 4 |
| RESEARCH | 2175.000000 | 4 |
±-----------±------------±------+

select 
    t.*,s.grade
from
    (select d.dname,avg(sal) as avgsal from emp e join dept d on e.deptno = d.deptno group by d.dname) t
join
    salgrade s
on
    t.avgsal between s.losal and s.hisal
where
    s.grade = (select grade from salgrade where (select avg(sal) as avgsal from emp group by deptno order by avgsal asc limit 1) between losal and hisal);

±------±------------±------+
| dname | avgsal | grade |
±------±------------±------+
| SALES | 1566.666667 | 3 |
±------±------------±------+

抛开之前的，最低等级你怎么着？
平均薪水最低的对应的等级一定是最低的.

select avg(sal) as avgsal from emp group by deptno order by avgsal asc limit 1;

±------------+
| avgsal |
±------------+
| 1566.666667 |
±------------+

select grade from salgrade where (select avg(sal) as avgsal from emp group by deptno order by avgsal asc limit 1) between losal and hisal;

±------+
| grade |
±------+
| 3 |
±------+

8、取得比普通员工(员工代码没有在 mgr 字段上出现的) 的最高薪水还要高的领导人姓名

比“普通员工的最高薪水”还要高的一定是领导！
没毛病！！！！

mysql> select distinct mgr from emp where mgr is not null;

±-----+
| mgr |
±-----+
| 7902 |
| 7698 |
| 7839 |
| 7566 |
| 7788 |
| 7782 |
±-----+
员工编号没有在以上范围内的都是普通员工。

第一步：找出普通员工的最高薪水！
not in在使用的时候，后面小括号中记得排除NULL。

select max(sal) from emp where empno not in(select distinct mgr from emp where mgr is not null);

±---------+
| max(sal) |
±---------+
| 1600.00 |
±---------+

第二步：找出高于1600的

select ename,sal from emp where sal > (select max(sal) from emp where empno not in(select distinct mgr from emp where mgr is not null));

±------±--------+
| ename | sal |
±------±--------+
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| SCOTT | 3000.00 |
| KING | 5000.00 |
| FORD | 3000.00 |
±------±--------+

9、取得薪水最高的前五名员工

select ename,sal from emp order by sal desc limit 5;

±------±--------+
| ename | sal |
±------±--------+
| KING | 5000.00 |
| SCOTT | 3000.00 |
| FORD | 3000.00 |
| JONES | 2975.00 |
| BLAKE | 2850.00 |
±------±--------+

10、取得薪水最高的第六到第十名员工

select ename,sal from emp order by sal desc limit 5, 5;

±-------±--------+
| ename | sal |
±-------±--------+
| CLARK | 2450.00 |
| ALLEN | 1600.00 |
| TURNER | 1500.00 |
| MILLER | 1300.00 |
| MARTIN | 1250.00 |
±-------±--------+

11、取得最后入职的 5 名员工

日期也可以降序，升序。

select ename,hiredate from emp order by hiredate desc limit 5;

±-------±-----------+
| ename | hiredate |
±-------±-----------+
| ADAMS | 1987-05-23 |
| SCOTT | 1987-04-19 |
| MILLER | 1982-01-23 |
| FORD | 1981-12-03 |
| JAMES | 1981-12-03 |
±-------±-----------+

12、取得每个薪水等级有多少员工

分组count

第一步：找出每个员工的薪水等级

select 
    e.ename,e.sal,s.grade 
from 
    emp e 
join 
    salgrade s 
on 
    e.sal between s.losal and s.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 |
±-------±--------±------+

第二步：继续按照grade分组统计数量

select 
    s.grade ,count(*)
from 
    emp e 
join 
    salgrade s 
on 
    e.sal between s.losal and s.hisal
group by
    s.grade;

±------±---------+
| grade | count(*) |
±------±---------+
| 1 | 3 |
| 2 | 3 |
| 3 | 2 |
| 4 | 5 |
| 5 | 1 |
±------±---------+

13、面试题：

有 3 个表 S(学生表)，C（课程表），SC（学生选课表）
S（SNO，SNAME）代表（学号，姓名）
C（CNO，CNAME，CTEACHER）代表（课号，课名，教师）
SC（SNO，CNO，SCGRADE）代表（学号，课号，成绩）
问题：
1，找出没选过“黎明”老师的所有学生姓名。
2，列出 2 门以上（含2 门）不及格学生姓名及平均成绩。
3，即学过 1 号课程又学过 2 号课所有学生的姓名。

14、列出所有员工及领导的姓名

select 
    a.ename '员工', b.ename '领导'
from
    emp a
left join
    emp b
on
    a.mgr = b.empno;

±-------±------+
| 员工 | 领导 |
±-------±------+
| SMITH | FORD |
| ALLEN | BLAKE |
| WARD | BLAKE |
| JONES | KING |
| MARTIN | BLAKE |
| BLAKE | KING |
| CLARK | KING |
| SCOTT | JONES |
| KING | NULL |
| TURNER | BLAKE |
| ADAMS | SCOTT |
| JAMES | BLAKE |
| FORD | JONES |
| MILLER | CLARK |
±-------±------+

15、列出受雇日期早于其直接上级的所有员工的编号,姓名,部门名称

emp a 员工表
emp b 领导表
a.mgr = b.empno and a.hiredate < b.hiredate

select 
    a.ename '员工', a.hiredate, b.ename '领导', b.hiredate, d.dname
from
    emp a
join
    emp b
on
    a.mgr = b.empno
join
    dept d
on
    a.deptno = d.deptno
where
     a.hiredate < b.hiredate;

±------±-----------±------±-----------±-----------+
| 员工 | hiredate | 领导 | hiredate | dname |
±------±-----------±------±-----------±-----------+
| CLARK | 1981-06-09 | KING | 1981-11-17 | ACCOUNTING |
| SMITH | 1980-12-17 | FORD | 1981-12-03 | RESEARCH |
| JONES | 1981-04-02 | KING | 1981-11-17 | RESEARCH |
| ALLEN | 1981-02-20 | BLAKE | 1981-05-01 | SALES |
| WARD | 1981-02-22 | BLAKE | 1981-05-01 | SALES |
| BLAKE | 1981-05-01 | KING | 1981-11-17 | SALES |
±------±-----------±------±-----------±-----------+

16、 列出部门名称和这些部门的员工信息, 同时列出那些没有员工的部门

select 
    e.*,d.dname
from
    emp e
right join
    dept d
on
    e.deptno = d.deptno;

±------±-------±----------±-----±-----------±--------±--------±-------±-----------+
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO | dname |
±------±-------±----------±-----±-----------±--------±--------±-------±-----------+
| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 | ACCOUNTING |
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 | ACCOUNTING |
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 | ACCOUNTING |
| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 | RESEARCH |
| 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 | RESEARCH |
| 7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 | RESEARCH |
| 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 | RESEARCH |
| 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 | RESEARCH |
| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 | SALES |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 | SALES |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 | SALES |
| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 | SALES |
| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 | SALES |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 | SALES |
| NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | OPERATIONS |
±------±-------±----------±-----±-----------±--------±--------±-------±-----------+

17、列出至少有 5 个员工的所有部门

按照部门编号分组，计数，筛选出 >= 5

select 
    deptno
from
    emp
group by
    deptno
having
    count(*) >= 5;

±-------+
| deptno |
±-------+
| 20 |
| 30 |
±-------+

18、列出薪金比"SMITH" 多的所有员工信息

select ename,sal from emp where sal > (select sal from emp where ename = 'SMITH');

±-------±--------+
| ename | sal |
±-------±--------+
| ALLEN | 1600.00 |
| WARD | 1250.00 |
| JONES | 2975.00 |
| MARTIN | 1250.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| SCOTT | 3000.00 |
| KING | 5000.00 |
| TURNER | 1500.00 |
| ADAMS | 1100.00 |
| JAMES | 950.00 |
| FORD | 3000.00 |
| MILLER | 1300.00 |
±-------±--------+

19、 列出所有"CLERK"( 办事员) 的姓名及其部门名称, 部门的人数

select ename,job from emp where job = 'CLERK';

±-------±------+
| ename | job |
±-------±------+
| SMITH | CLERK |
| ADAMS | CLERK |
| JAMES | CLERK |
| MILLER | CLERK |
±-------±------+

select 
    e.ename,e.job,d.dname
from 
    emp e
join
    dept d
on
    e.deptno = d.deptno
where 
    e.job = 'CLERK';

±-------±------±-----------+
| ename | job | dname |
±-------±------±-----------+
| MILLER | CLERK | ACCOUNTING |
| SMITH | CLERK | RESEARCH |
| ADAMS | CLERK | RESEARCH |
| JAMES | CLERK | SALES |
±-------±------±-----------+

select 
    e.ename,e.job,d.dname,d.deptno
from 
    emp e
join
    dept d
on
    e.deptno = d.deptno
where 
    e.job = 'CLERK';

±-------±------±-----------±-------+
| ename | job | dname | deptno |
±-------±------±-----------±-------+
| MILLER | CLERK | ACCOUNTING | 10 |
| SMITH | CLERK | RESEARCH | 20 |
| ADAMS | CLERK | RESEARCH | 20 |
| JAMES | CLERK | SALES | 30 |
±-------±------±-----------±-------+

//每个部门的人数？

select deptno, count(*) as deptcount from emp group by deptno;

±-------±----------+
| deptno | deptcount |
±-------±----------+
| 10 | 3 |
| 20 | 5 |
| 30 | 6 |
±-------±----------+

select 
    t1.*,t2.deptcount
from
    (select 
        e.ename,e.job,d.dname,d.deptno
    from 
        emp e
    join
        dept d
    on
        e.deptno = d.deptno
    where 
        e.job = 'CLERK') t1
join
    (select deptno, count(*) as deptcount from emp group by deptno) t2
on
    t1.deptno = t2.deptno;

±-------±------±-----------±-------±----------+
| ename | job | dname | deptno | deptcount |
±-------±------±-----------±-------±----------+
| MILLER | CLERK | ACCOUNTING | 10 | 3 |
| SMITH | CLERK | RESEARCH | 20 | 5 |
| ADAMS | CLERK | RESEARCH | 20 | 5 |
| JAMES | CLERK | SALES | 30 | 6 |
±-------±------±-----------±-------±----------+

20、列出最低薪金大于 1500 的各种工作及从事此工作的全部雇员人数 按照工作岗位分组求最小值。

select job,count(*) from emp group by job having min(sal) > 1500;

±----------±---------+
| job | count(*) |
±----------±---------+
| ANALYST | 2 |
| MANAGER | 3 |
| PRESIDENT | 1 |
±----------±---------+

21、列出在部门"SALES"< 销售部> 工作的员工的姓名, 假定不知道销售部的部门编号.

select ename from emp where deptno = (select deptno from dept where dname = 'SALES');

±-------+
| ename |
±-------+
| ALLEN |
| WARD |
| MARTIN |
| BLAKE |
| TURNER |
| JAMES |
±-------+

22、列出薪金高于公司平均薪金的所有员工, 所在部门, 上级领导, 雇员的工资等级.

select 
    e.ename '员工',d.dname,l.ename '领导',s.grade
from
    emp e
join
    dept d
on
    e.deptno = d.deptno
left join
    emp l
on
    e.mgr = l.empno
join
    salgrade s
on
    e.sal between s.losal and s.hisal
where
    e.sal > (select avg(sal) from emp);

±------±-----------±------±------+
| 员工 | dname | 领导 | grade |
±------±-----------±------±------+
| JONES | RESEARCH | KING | 4 |
| BLAKE | SALES | KING | 4 |
| CLARK | ACCOUNTING | KING | 4 |
| SCOTT | RESEARCH | JONES | 4 |
| KING | ACCOUNTING | NULL | 5 |
| FORD | RESEARCH | JONES | 4 |
±------±-----------±------±------+

23、 列出与"SCOTT" 从事相同工作的所有员工及部门名称

select job from emp where ename = 'SCOTT';

±--------+
| job |
±--------+
| ANALYST |
±--------+

select 
    e.ename,e.job,d.dname
from
    emp e
join
    dept d
on
    e.deptno = d.deptno
where
    e.job = (select job from emp where ename = 'SCOTT')
and
    e.ename <> 'SCOTT';

±------±--------±---------+
| ename | job | dname |
±------±--------±---------+
| FORD | ANALYST | RESEARCH |
±------±--------±---------+

24、列出薪金等于部门 30 中员工的薪金的其他员工的姓名和薪金.

select distinct sal from emp where deptno = 30;

±--------+
| sal |
±--------+
| 1600.00 |
| 1250.00 |
| 2850.00 |
| 1500.00 |
| 950.00 |
±--------+

select 
    ename,sal 
from 
    emp 
where 
    sal in(select distinct sal from emp where deptno = 30) 
and 
    deptno <> 30;

Empty set (0.00 sec)

25、列出薪金高于在部门 30 工作的所有员工的薪金的员工姓名和薪金. 部门名称

select max(sal) from emp where deptno = 30;

±---------+
| max(sal) |
±---------+
| 2850.00 |
±---------+

select
    e.ename,e.sal,d.dname
from
    emp e
join
    dept d
on
    e.deptno = d.deptno
where
    e.sal > (select max(sal) from emp where deptno = 30);

±------±--------±-----------+
| ename | sal | dname |
±------±--------±-----------+
| KING | 5000.00 | ACCOUNTING |
| JONES | 2975.00 | RESEARCH |
| SCOTT | 3000.00 | RESEARCH |
| FORD | 3000.00 | RESEARCH |
±------±--------±-----------+

26、列出在每个部门工作的员工数量, 平均工资和平均服务期限

没有员工的部门，部门人数是0

select 
    d.deptno, count(e.ename) ecount,ifnull(avg(e.sal),0) as avgsal, ifnull(avg(timestampdiff(YEAR, hiredate, now())), 0) as avgservicetime
from
    emp e
right join
    dept d
on
    e.deptno = d.deptno
group by
    d.deptno;

±-------±-------±------------±---------------+
| deptno | ecount | avgsal | avgservicetime |
±-------±-------±------------±---------------+
| 10 | 3 | 2916.666667 | 38.0000 |
| 20 | 5 | 2175.000000 | 35.8000 |
| 30 | 6 | 1566.666667 | 38.3333 |
| 40 | 0 | 0.000000 | 0.0000 |
±-------±-------±------------±---------------+

在mysql当中怎么计算两个日期的“年差”，差了多少年？

TimeStampDiff(间隔类型, 前一个日期, 后一个日期)

timestampdiff(YEAR, hiredate, now())

间隔类型：
SECOND 秒，
MINUTE 分钟，
HOUR 小时，
DAY 天，
WEEK 星期
MONTH 月，
QUARTER 季度，
YEAR 年

27、 列出所有员工的姓名、部门名称和工资。

select 
    e.ename,d.dname,e.sal
from
    emp e
join 
    dept d
on
    e.deptno = d.deptno;

±-------±-----------±--------+
| ename | dname | sal |
±-------±-----------±--------+
| CLARK | ACCOUNTING | 2450.00 |
| KING | ACCOUNTING | 5000.00 |
| MILLER | ACCOUNTING | 1300.00 |
| SMITH | RESEARCH | 800.00 |
| JONES | RESEARCH | 2975.00 |
| SCOTT | RESEARCH | 3000.00 |
| ADAMS | RESEARCH | 1100.00 |
| FORD | RESEARCH | 3000.00 |
| ALLEN | SALES | 1600.00 |
| WARD | SALES | 1250.00 |
| MARTIN | SALES | 1250.00 |
| BLAKE | SALES | 2850.00 |
| TURNER | SALES | 1500.00 |
| JAMES | SALES | 950.00 |
±-------±-----------±--------+

28、列出所有部门的详细信息和人数

select 
    d.deptno,d.dname,d.loc,count(e.ename)
from
    emp e
right join
    dept d
on
    e.deptno = d.deptno
group by
    d.deptno,d.dname,d.loc;

±-------±-----------±---------±---------------+
| deptno | dname | loc | count(e.ename) |
±-------±-----------±---------±---------------+
| 10 | ACCOUNTING | NEW YORK | 3 |
| 20 | RESEARCH | DALLAS | 5 |
| 30 | SALES | CHICAGO | 6 |
| 40 | OPERATIONS | BOSTON | 0 |
±-------±-----------±---------±---------------+

29、列出各种工作的最低工资及从事此工作的雇员姓名

select 
    job,min(sal) as minsal
from
    emp
group by
    job;

±----------±---------+
| job | minsal |
±----------±---------+
| ANALYST | 3000.00 |
| CLERK | 800.00 |
| MANAGER | 2450.00 |
| PRESIDENT | 5000.00 |
| SALESMAN | 1250.00 |
±----------±---------+

emp e和以上t连接

select 
    e.ename,t.*
from
    emp e
join
    (select 
        job,min(sal) as minsal
    from
        emp
    group by
        job) t
on
    e.job = t.job and e.sal = t.minsal;

±-------±----------±--------+
| ename | job | minsal |
±-------±----------±--------+
| SMITH | CLERK | 800.00 |
| WARD | SALESMAN | 1250.00 |
| MARTIN | SALESMAN | 1250.00 |
| CLARK | MANAGER | 2450.00 |
| SCOTT | ANALYST | 3000.00 |
| KING | PRESIDENT | 5000.00 |
| FORD | ANALYST | 3000.00 |
±-------±----------±--------+

30、列出各个部门的 MANAGER( 领导) 的最低薪金

select 
    deptno, min(sal)
from
    emp
where
    job = 'MANAGER'
group by
    deptno;

±-------±---------+
| deptno | min(sal) |
±-------±---------+
| 10 | 2450.00 |
| 20 | 2975.00 |
| 30 | 2850.00 |
±-------±---------+

31、列出所有员工的 年工资, 按 年薪从低到高排序

select 
    ename,(sal + ifnull(comm,0)) * 12 as yearsal
from
    emp
order by
    yearsal asc;

±-------±---------+
| ename | yearsal |
±-------±---------+
| SMITH | 9600.00 |
| JAMES | 11400.00 |
| ADAMS | 13200.00 |
| MILLER | 15600.00 |
| TURNER | 18000.00 |
| WARD | 21000.00 |
| ALLEN | 22800.00 |
| CLARK | 29400.00 |
| MARTIN | 31800.00 |
| BLAKE | 34200.00 |
| JONES | 35700.00 |
| FORD | 36000.00 |
| SCOTT | 36000.00 |
| KING | 60000.00 |
±-------±---------+

32、求出员工领导的薪水超过3000的员工名称与领导

select 
    a.ename '员工',b.ename '领导'
from
    emp a
join
    emp b
on
    a.mgr = b.empno
where
    b.sal > 3000;

±------±-----+
| 员工 | 领导 |
±------±-----+
| JONES | KING |
| BLAKE | KING |
| CLARK | KING |
±------±-----+

33、求出部门名称中, 带’S’字符的部门员工的工资合计、部门人数

select 
    d.deptno,d.dname,d.loc,count(e.ename),ifnull(sum(e.sal),0) as sumsal
from
    emp e
right join
    dept d
on
    e.deptno = d.deptno
where
    d.dname like '%S%'
group by
    d.deptno,d.dname,d.loc;

±-------±-----------±--------±---------------±---------+
| deptno | dname | loc | count(e.ename) | sumsal |
±-------±-----------±--------±---------------±---------+
| 20 | RESEARCH | DALLAS | 5 | 10875.00 |
| 30 | SALES | CHICAGO | 6 | 9400.00 |
| 40 | OPERATIONS | BOSTON | 0 | 0.00 |
±-------±-----------±--------±---------------±---------+

34、给任职日期超过 30 年的员工加薪 10%.

update emp set sal = sal * 1.1 where timestampdiff(YEAR, hiredate, now()) > 30;

最后感谢大家的支持
在这里插入图片描述

标签： 数据库 mysql
本文转载自: https://blog.csdn.net/qq_57013916/article/details/123973703
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