“做程序员，圈子和学习最重要”因为有有了圈子可以让你少走弯路，扩宽人脉，扩展思路，学习他人的一些经验及学习方法！同时在这分享一下是一直以来整理的Java后端进阶笔记文档和学习资料免费分享给大家！需要资料的朋友私信我扣【06】TEST
数据库描述
mysql> show tables;
+-----------------------+
| Tables_in_bjpowernode |
+-----------------------+
| dept |
| emp |
| salgrade |
+-----------------------+
mysql> select DEPTNO,DNAME,LOC from dept;
+--------+------------+----------+
| DEPTNO | DNAME | LOC |
+--------+------------+----------+
| 10 | ACCOUNTING | NEW YORK |
| 20 | RESEARCH | DALLAS |
| 30 | SALES | CHICAGO |
| 40 | OPERATIONS | BOSTON |
+--------+------------+----------+
mysql> select * from emp; // 开发中最好不要使用 * (效率低)
+-------+--------+-----------+------+------------+---------+---------+--------+
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
+-------+--------+-----------+------+------------+---------+---------+--------+
| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 |
| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 |
| 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 |
| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 |
| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 |
| 7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 |
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 |
| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 |
| 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 |
| 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 |
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 |
+-------+--------+-----------+------+------------+---------+---------+--------+
mysql> select * from salgrade;
+-------+-------+-------+
| GRADE | LOSAL | HISAL |
+-------+-------+-------+
| 1 | 700 | 1200 |
| 2 | 1201 | 1400 |
| 3 | 1401 | 2000 |
| 4 | 2001 | 3000 |
| 5 | 3001 | 9999 |
+-------+-------+-------+
Test1
# 题意：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（按部门编号分组，找出每一组的最大值）
select
deptno,max(sal) as maxsal
from
emp
group by
deptno;
+--------+---------+
| deptno | maxsal |
+--------+---------+
| 20 | 3000.00 |
| 30 | 2850.00 |
| 10 | 5000.00 |
+--------+---------+
第二步：将以上查询结果看成一张临时表 t，连接 t 和 emp，
条件：emp.deptno = t.deptno and emp.sal = t.maxsal
从而得到每个部门最高薪水的人员名称。
select
e.ename, t.deptno, t.maxsal
from
emp e
join
(select deptno,max(sal) as maxsal from emp group by deptno) t
on
e.deptno = t.deptno and e.sal = t.maxsal;
+-------+--------+---------+
| ename | deptno | maxsal |
+-------+--------+---------+
| BLAKE | 30 | 2850.00 |
| SCOTT | 20 | 3000.00 |
| KING | 10 | 5000.00 |
| FORD | 20 | 3000.00 |
+-------+--------+---------+
Test2
# 题意：取出薪水在部门的平均薪水之上的人员名称
第一步：找出每个部门的平均薪水
mysql> select deptno,avg(sal) as avgsal from emp group by deptno;
+--------+-------------+
| deptno | avgsal |
+--------+-------------+
| 20 | 2175.000000 |
| 30 | 1566.666667 |
| 10 | 2916.666667 |
+--------+-------------+
第二步：将上述查询结果作为一张临时表 t，连接 t 和 emp e
条件为：e.deptno = t.deptno and e.sal > t.avgsal
select
e.ename,e.sal,t.deptno,t.avgsal
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;
+-------+---------+--------+-------------+
| ename | sal | deptno | avgsal |
+-------+---------+--------+-------------+
| ALLEN | 1600.00 | 30 | 1566.666667 |
| JONES | 2975.00 | 20 | 2175.000000 |
| BLAKE | 2850.00 | 30 | 1566.666667 |
| SCOTT | 3000.00 | 20 | 2175.000000 |
| KING | 5000.00 | 10 | 2916.666667 |
| FORD | 3000.00 | 20 | 2175.000000 |
+-------+---------+--------+-------------+
Test3
# 取出部门中（所有人）平均的薪水等级
第一步：取出所有人的薪水等级
select
e.ename,e.deptno,e.sal,t.grade
from
emp e
join
salgrade t
on
e.sal between t.losal and t.hisal;
+--------+--------+---------+-------+
| ename | deptno | sal | grade |
+--------+--------+---------+-------+
| SMITH | 20 | 800.00 | 1 |
| ALLEN | 30 | 1600.00 | 3 |
| WARD | 30 | 1250.00 | 2 |
| JONES | 20 | 2975.00 | 4 |
| MARTIN | 30 | 1250.00 | 2 |
| BLAKE | 30 | 2850.00 | 4 |
| CLARK | 10 | 2450.00 | 4 |
| SCOTT | 20 | 3000.00 | 4 |
| KING | 10 | 5000.00 | 5 |
| TURNER | 30 | 1500.00 | 3 |
| ADAMS | 20 | 1100.00 | 1 |
| JAMES | 30 | 950.00 | 1 |
| FORD | 20 | 3000.00 | 4 |
| MILLER | 10 | 1300.00 | 2 |
+--------+--------+---------+-------+
第二步：按照部门编号分组，取得每个部门的平均的薪水等级
select e.deptno,avg(t.grade) as avg_grade
from
emp e
join
salgrade t
on
e.sal between t.losal and t.hisal
group by
e.deptno
order by
e.deptno;
+--------+-----------+
| deptno | avg_grade |
+--------+-----------+
| 10 | 3.6667 |
| 20 | 2.8000 |
| 30 | 2.5000 |
+--------+-----------+
Test4
# 题意：取得最高薪水
方案一：
select
ename,sal
from
emp
order by
sal desc
limit # limit 需要注意可能存在两个一样的最高薪水（若需要求最高薪水对于的员工名称的话）
1;
+-------+---------+
| ename | sal |
+-------+---------+
| KING | 5000.00 |
+-------+---------+
方案二：
step1: select max(sal) as max_sal from emp;
+---------+
| max_sal |
+---------+
| 5000.00 |
+---------+
step2: select ename,sal from emp where sal = (select max(sal) as max_sal from emp);
+-------+---------+
| ename | sal |
+-------+---------+
| KING | 5000.00 |
+-------+---------+
方案三：(自连接)
step1:
select distinct a.sal from emp a join emp b on a.sal < b.sal;
+---------+
| sal |
+---------+
| 1300.00 |
| 950.00 |
| 1100.00 |
| 1500.00 |
| 1250.00 |
| 800.00 |
| 2450.00 |
| 2850.00 |
| 1600.00 |
| 2975.00 |
| 3000.00 |
+---------+
step2:
select ename,sal from emp
where
sal not in(select distinct a.sal from emp a join emp b on a.sal < b.sal);
+-------+---------+
| ename | sal |
+-------+---------+
| KING | 5000.00 |
+-------+---------+
Test5
# 题意：找出平均薪水最高的部门编号
# 方案一：
step1:
select deptno,avg(sal) as avg_sal from emp group by deptno;
+--------+-------------+
| deptno | avg_sal |
+--------+-------------+
| 20 | 2175.000000 |
| 30 | 1566.666667 |
| 10 | 2916.666667 |
+--------+-------------+
step2:
select deptno,avg(sal) as avg_sal from emp
group by deptno
order by avg_sal desc
limit 1; # 需要注意可能存在两个薪水一样且都是最高
+--------+-------------+
| deptno | avg_sal |
+--------+-------------+
| 10 | 2916.666667 |
+--------+-------------+
# 方案二：
step1：
select max(t.avg_sal) from (select deptno,avg(sal) as avg_sal from emp group by deptno) t;
调用每个派生表都必须有自己的别名！！！
ERROR 1248 (42000): Every derived table must have its own alias
+--------------+
| max(avg_sal) |
+--------------+
| 2916.666667 |
+--------------+
step2:
select
deptno,avg(sal) avg_sal
from
emp
group by
deptno
having
avg_sal = (select max(t.avg_sal) from (select deptno,avg(sal) as avg_sal from emp group by deptno) t);
+--------+-------------+
| deptno | avg_sal |
+--------+-------------+
| 10 | 2916.666667 |
+--------+-------------+
Test6
# 题意：取得平均薪水最高的部门的名称
select d.dname,avg(e.sal) as avg_sal
from emp e
join dept d
on e.deptno = d.deptno
group by d.dname
order by avg_sal desc
limit 1; # 需要注意平均薪水最高的部门可能有多个且它们的平均薪水一样，找出最高再用 where 筛选
+------------+-------------+
| dname | avg_sal |
+------------+-------------+
| ACCOUNTING | 2916.666667 |
+------------+-------------+
Test7
# 题意：求平均薪水的等级最低的部门的名称
两个点：
1.平均薪水最低等级一定最低
2.平均薪水不是最低，但其等级可能是最低
第一步：找出每个部门的平均薪水（按部门名称分类）
select d.dname,avg(e.sal) as avg_sal
from emp e
join dept d
on e.deptno = d.deptno
group by d.dname;
+------------+-------------+
| dname | avg_sal |
+------------+-------------+
| RESEARCH | 2175.000000 |
| SALES | 1566.666667 |
| ACCOUNTING | 2916.666667 |
+------------+-------------+
第二步：得到每个部门对应的平均薪水的等级
select
t.dname,t.avg_sal,s.grade
from
(select d.dname,avg(e.sal) as avg_sal from emp e join dept d on e.deptno = d.deptno group by d.dname) t
join
salgrade s
on
t.avg_sal between losal and hisal;
+------------+-------------+-------+
| dname | avg_sal | grade |
+------------+-------------+-------+
| RESEARCH | 2175.000000 | 4 |
| SALES | 1566.666667 | 3 |
| ACCOUNTING | 2916.666667 | 4 |
+------------+-------------+-------+
第三步：找出最低平均薪资所对应的等级
step1: 找出最低薪资
select avg(sal) as avg_sal from emp group by deptno order by avg_sal asc limit 1;
+-------------+
| avg_sal |
+-------------+
| 1566.666667 |
+-------------+
step2: 找出最低薪资对应的等级
select grade from salgrade
where
(select avg(sal) as avg_sal from emp group by deptno order by avg_sal asc limit 1) between losal and hisal;
+-------+
| grade |
+-------+
| 3 |
+-------+
第四步：找出平均薪水的等级最低的部门的名称
select t.dname,t.avg_sal,s.grade
from
(select d.dname,avg(e.sal) as avg_sal from emp e join dept d on e.deptno = d.deptno group by d.dname) t
join
salgrade s
on
t.avg_sal between losal and hisal
where
s.grade = (select grade from salgrade where
(select avg(sal) as avg_sal from emp group by deptno order by avg_sal asc limit 1) between losal and hisal);
+-------+-------------+-------+
| dname | avg_sal | grade |
+-------+-------------+-------+
| SALES | 1566.666667 | 3 |
+-------+-------------+-------+
Test8
# 题意：取得比普通员工（员工代码没有再 mgr 字段上出现的）的最高薪水还要高的领导姓名
第一步：找出领导（不在此区间的则为普通员工）
select distinct mgr from emp where mgr is not null; # 需要排除空值
+------+
| mgr |
+------+
| 7902 |
| 7698 |
| 7839 |
| 7566 |
| 7788 |
| 7782 |
+------+
第二步：找出普通员工的最高薪水
select max(sal) as maxsal from emp
where empno not in(select distinct mgr from emp where mgr is not null);
+---------+
| maxsal |
+---------+
| 1600.00 |
+---------+
第三步：找出比其最高薪水高的领导人姓名(需要注意：比普通员工的最高薪水还要高的一定是领导)
select ename,sal from emp
where
sal > (select max(sal) as maxsal 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 |
+-------+---------+
Test9
# 取得薪水最高的前五名员工（不考虑相等）
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 |
+-------+---------+
Test10
# 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 |
| WARD | 1250.00 |
+--------+---------+
Test11
# 取得最后入职的 5 名员工
注意：日期也可以排序
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 |
| JAMES | 1981-12-03 |
| FORD | 1981-12-03 |
+--------+------------+
Test12
# 取得每个薪水等级有多少个员工
第一步：取得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：取得每个薪水等级对应的员工个数（按薪水等级分组）
# select s.grade,count(*) # count(*) 只要一行记录中有一个不为 NULL 的都会被记录（即总记录数）
select s.grade,count(empno) as emp_count # 拿 empno 来计算员工的个数 因为 empn 为主键，不能为 NULL
from emp e
join salgrade s
on e.sal between s.losal and s.hisal
group by s.grade
order by s.grade;
+-------+-----------+
| grade | emp_count |
+-------+-----------+
| 1 | 3 |
| 2 | 3 |
| 3 | 2 |
| 4 | 5 |
| 5 | 1 |
+-------+-----------+
Test13
# 题意：
有三个表 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,CNAEM,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. 找出学过 1 号课程又学过 2 号课程所有学生的姓名
Test14
# 题意：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 (outer) join # 左外连接
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 |
+--------+-------+
Test15
# 题意：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
select a.empno,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;
+-------+-------+------------+-------+------------+------------+
| empno | 员工 | hiredate | 领导 | hiredate | dname |
+-------+-------+------------+-------+------------+------------+
| 7369 | SMITH | 1980-12-17 | FORD | 1981-12-03 | RESEARCH |
| 7499 | ALLEN | 1981-02-20 | BLAKE | 1981-05-01 | SALES |
| 7521 | WARD | 1981-02-22 | BLAKE | 1981-05-01 | SALES |
| 7566 | JONES | 1981-04-02 | KING | 1981-11-17 | RESEARCH |
| 7698 | BLAKE | 1981-05-01 | KING | 1981-11-17 | SALES |
| 7782 | CLARK | 1981-06-09 | KING | 1981-11-17 | ACCOUNTING |
+-------+-------+------------+-------+------------+------------+
Test16
# 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 # 右外连接 以部门表为主表（因为题意需要列出没有员工的部门）
on e.deptno = d.deptno;
+-------+--------+-----------+------+------------+---------+---------+--------+------------+
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO | dname |
+-------+--------+-----------+------+------------+---------+---------+--------+------------+
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 | ACCOUNTING |
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 | ACCOUNTING |
| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 | ACCOUNTING |
| 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 | RESEARCH |
| 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 | RESEARCH |
| 7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 | RESEARCH |
| 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 | RESEARCH |
| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 | RESEARCH |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 | SALES |
| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 | SALES |
| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 | SALES |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 | SALES |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 | SALES |
| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 | SALES |
| NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | OPERATIONS |
+-------+--------+-----------+------+------------+---------+---------+--------+------------+
Test17
# 题意：列出至少有 5 个员工的部门
select d.dname,count(*)
from emp e
join dept d
on e.deptno = d.deptno
group by d.dname
having count(*) >= 5;
+----------+----------+
| dname | count(*) |
+----------+----------+
| RESEARCH | 5 |
| SALES | 6 |
+----------+----------+
Test18
# 题意：列出薪资比‘SMITH’多的所有员工信息
第一步：找出'SMITH'的薪资
select sal from emp where ename = 'SMITH';
+--------+
| sal |
+--------+
| 800.00 |
+--------+
第二步：找出比其薪资大的所有员工的信息
select * from emp where sal > (select sal from emp where ename = 'SMITH');
+-------+--------+-----------+------+------------+---------+---------+--------+
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
+-------+--------+-----------+------+------------+---------+---------+--------+
| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 |
| 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 |
| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 |
| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 |
| 7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 |
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 |
| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 |
| 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 |
| 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 |
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 |
+-------+--------+-----------+------+------------+---------+---------+--------+
Test19
# 题意：列出所有'CLERK'（办事员）的姓名及其部门名称，部门的人数
第一步：找出办事员的姓名及其部门名称
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 |
+--------+-------+------------+--------+
| SMITH | CLERK | RESEARCH | 20 |
| ADAMS | CLERK | RESEARCH | 20 |
| JAMES | CLERK | SALES | 30 |
| MILLER | CLERK | ACCOUNTING | 10 |
+--------+-------+------------+--------+
第二步：找出部门名称及其人数()
select d.dname,count(*) as emp_count
from emp e
join dept d
on e.deptno = d.deptno
group by d.dname;
+------------+-----------+
| dname | emp_count |
+------------+-----------+
| RESEARCH | 5 |
| SALES | 6 |
| ACCOUNTING | 3 |
+------------+-----------+
第三步：列出所有办事员的姓名及其部门名称，部门的人数
select a.ename,a.job,a.dname,a.deptno,b.emp_count
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') a
join
(select d.dname,count(*) as emp_count from emp e join dept d on e.deptno = d.deptno group by d.dname) b
on
a.dname = b.dname;
+--------+-------+------------+--------+-----------+
| ename | job | dname | deptno | emp_count |
+--------+-------+------------+--------+-----------+
| SMITH | CLERK | RESEARCH | 20 | 5 |
| ADAMS | CLERK | RESEARCH | 20 | 5 |
| JAMES | CLERK | SALES | 30 | 6 |
| MILLER | CLERK | ACCOUNTING | 10 | 3 |
+--------+-------+------------+--------+-----------+
Test20
# 题意：列出最低薪资大于 1500 的各种工作及从事此工作的全部雇员人数
第一步：找出最低薪资大于 1500 的各种工作
select job,min(sal) as min_sal from emp group by job having min(sal) > 1500;
+-----------+---------+
| job | min_sal |
+-----------+---------+
| MANAGER | 2450.00 |
| ANALYST | 3000.00 |
| PRESIDENT | 5000.00 |
+-----------+---------+
第二步：列出最低薪资大于 1500 的各种工作及其对应的全部雇员人数
select
job,min(sal) as min_sal,count(*) as emp_count
from
emp
group by
job
having
min(sal) > 1500;
+-----------+---------+-----------+
| job | min_sal | emp_count |
+-----------+---------+-----------+
| MANAGER | 2450.00 | 3 |
| ANALYST | 3000.00 | 2 |
| PRESIDENT | 5000.00 | 1 |
+-----------+---------+-----------+
Test21
# 题意：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
第一步：找出部门'SALES'的部门编号
select deptno from dept where dname = 'SALES';
第二步：找出在部门'SALES'的员工姓名
select e.ename,d.dname
from emp e
join dept d
on e.deptno = d.deptno
where e.deptno = (select deptno from dept where dname = 'SALES');
+--------+-------+
| ename | dname |
+--------+-------+
| ALLEN | SALES |
| WARD | SALES |
| MARTIN | SALES |
| BLAKE | SALES |
| TURNER | SALES |
| JAMES | SALES |
+--------+-------+
Test22
# 题意：列出薪资高于公司平均薪资的所有员工，所在部门，上级领导，雇员的工资等级
第一步：找出公司的平均薪资
select avg(sal) from emp;
+-------------+
| avg(sal) |
+-------------+
| 2073.214286 |
+-------------+
第二步：列出薪资高于公司平均薪资的所有员工，所在部门，上级领导，雇员的工资等级
select a.ename '员工',a.deptno,d.dname,b.ename '领导',s.grade
from emp a
join dept d
on a.deptno = d.deptno
left join emp b
on a.mgr = b.empno
join salgrade s
on a.sal between losal and hisal
where a.sal > (select avg(sal) from emp);
+-------+--------+------------+-------+-------+
| 员工 | deptno | dname | 领导 | grade |
+-------+--------+------------+-------+-------+
| FORD | 20 | RESEARCH | JONES | 4 |
| SCOTT | 20 | RESEARCH | JONES | 4 |
| CLARK | 10 | ACCOUNTING | KING | 4 |
| BLAKE | 30 | SALES | KING | 4 |
| JONES | 20 | RESEARCH | KING | 4 |
| KING | 10 | ACCOUNTING | NULL | 5 |
+-------+--------+------------+-------+-------+
Test23
# 题意：列出与'SCOTT'（员工名）从事相同工作的所有员工及部门名称
第一步：找出 'SCOTT' 的工作
select job from emp where ename = 'SCOTT';
+---------+
| job |
+---------+
| ANALYST |
+---------+
第二步：列出与'SCOTT'（员工名）从事相同工作的所有员工及部门名称
select e.ename,e.deptno,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 | deptno | dname |
+-------+--------+----------+
| FORD | 20 | RESEARCH |
+-------+--------+----------+
Test24
# 题意：列出薪资等于部门 30 中员工的薪资的其他员工的姓名和薪资
第一步：列出部门 30 的员工的薪资
select distinct sal from emp where deptno = 30;
+---------+
| sal |
+---------+
| 1600.00 |
| 1250.00 |
| 2850.00 |
| 1500.00 |
| 950.00 |
+---------+
第二步：列出薪资等于部门 30 中员工的薪资的其他员工的姓名和薪资
select ename,sal
from emp
where sal in (select sal from emp where deptno = 30)
and deptno <> 30;
Empty set (0.00 sec)
Test25
# 题意：列出薪资高于在部门 30 工作的所有员工的薪资的员工的姓名，薪资和部门名称
第一步：找出在部门 30 工作的员工的最高薪资
select max(sal) from emp where deptno = 30;
select max(sal) from emp group by deptno having deptno = 30; # 这种方法效率较低
第二步：列出薪资高于在部门 30 工作的所有员工的薪资的员工的姓名，薪资和部门名称
select e.ename,e.sal,e.deptno,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 | deptno | dname |
+-------+---------+--------+------------+
| JONES | 2975.00 | 20 | RESEARCH |
| SCOTT | 3000.00 | 20 | RESEARCH |
| KING | 5000.00 | 10 | ACCOUNTING |
| FORD | 3000.00 | 20 | RESEARCH |
+-------+---------+--------+------------+
Test26
# 题意：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
count 自动忽略 NULL
timestampdiff(间隔类型，开始时间，结束时间)
间隔类型有：year，quarter，month，week，day，hour，minute，second
以部门表为主表：
select
d.deptno,d.dname,count(e.empno) as emp_count, ifnull(avg(e.sal),0) as avg_sal,
avg(ifnull(timestampdiff(day,e.hiredate,now()),0)) as avg_servtime
from emp e
right join dept d
on e.deptno = d.deptno
group by d.dname;
+------------+-----------+-------------+--------------+
| dname | emp_count | avg_sal | avg_servtime |
+------------+-----------+-------------+--------------+
| ACCOUNTING | 3 | 2916.666667 | 14798.3333 |
| RESEARCH | 5 | 2175.000000 | 14078.2000 |
| SALES | 6 | 1566.666667 | 14907.3333 |
| OPERATIONS | 0 | 0.000000 | 0.0000 |
+------------+-----------+-------------+--------------+
Test27
# 题意：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 |
+--------+------------+---------+
| SMITH | RESEARCH | 800.00 |
| ALLEN | SALES | 1600.00 |
| WARD | SALES | 1250.00 |
| JONES | RESEARCH | 2975.00 |
| MARTIN | SALES | 1250.00 |
| BLAKE | SALES | 2850.00 |
| CLARK | ACCOUNTING | 2450.00 |
| SCOTT | RESEARCH | 3000.00 |
| KING | ACCOUNTING | 5000.00 |
| TURNER | SALES | 1500.00 |
| ADAMS | RESEARCH | 1100.00 |
| JAMES | SALES | 950.00 |
| FORD | RESEARCH | 3000.00 |
| MILLER | ACCOUNTING | 1300.00 |
+--------+------------+---------+
Test28
# 题意：列出所有部门的详细信息和人数
select d.deptno,d.dname,d.loc,count(e.empno) as emp_count
from emp e
right join dept d
on e.deptno = d.deptno
group by d.deptno,d.dname,d.loc;
+--------+------------+----------+-----------+
| deptno | dname | loc | emp_count |
+--------+------------+----------+-----------+
| 10 | ACCOUNTING | NEW YORK | 3 |
| 20 | RESEARCH | DALLAS | 5 |
| 30 | SALES | CHICAGO | 6 |
| 40 | OPERATIONS | BOSTON | 0 |
+--------+------------+----------+-----------+
Test29
# 题意：列出各种工作的最低工资及从事此工作的员工姓名
第一步：列出各种工作的最低工资
select job,min(sal) as min_sal
from emp
group by job;
+-----------+---------+
| job | min_sal |
+-----------+---------+
| CLERK | 800.00 |
| SALESMAN | 1250.00 |
| MANAGER | 2450.00 |
| ANALYST | 3000.00 |
| PRESIDENT | 5000.00 |
+-----------+---------+
第二步：列出各种工作的最低工资及从事此工作的员工姓名
select e.ename,a.job,a.min_sal
from emp e
join (select job,min(sal) as min_sal from emp group by job) a
on a.job = e.job and a.min_sal = e.sal
order by a.min_sal;
+--------+-----------+---------+
| ename | job | min_sal |
+--------+-----------+---------+
| SMITH | CLERK | 800.00 |
| WARD | SALESMAN | 1250.00 |
| MARTIN | SALESMAN | 1250.00 |
| CLARK | MANAGER | 2450.00 |
| SCOTT | ANALYST | 3000.00 |
| FORD | ANALYST | 3000.00 |
| KING | PRESIDENT | 5000.00 |
+--------+-----------+---------+
Test30
# 题意：列出各个部门的 MANAGER（领导）的最低薪资
第一步：简略列出各个部门 MANAGER 的最低薪资
select d.deptno,d.dname,min(e.sal) as min_sal
from emp e
join dept d
on e.deptno = d.deptno
where job = 'MANAGER'
group by d.deptno,d.dname
order by d.deptno;
+--------+------------+---------+
| deptno | dname | min_sal |
+--------+------------+---------+
| 10 | ACCOUNTING | 2450.00 |
| 20 | RESEARCH | 2975.00 |
| 30 | SALES | 2850.00 |
+--------+------------+---------+
第二步：详细列出各个部门 MANAGER 的最低薪资
select
e.ename,e.job,t.deptno,t.dname,t.min_sal
from
emp e
join
(select d.deptno,d.dname,min(e.sal) as min_sal from emp e join dept d on e.deptno = d.deptno where job = 'MANAGER' group by d.deptno,d.dname order by d.deptno) t
on e.sal = t.min_sal;
+-------+---------+--------+------------+---------+
| ename | job | deptno | dname | min_sal |
+-------+---------+--------+------------+---------+
| JONES | MANAGER | 20 | RESEARCH | 2975.00 |
| BLAKE | MANAGER | 30 | SALES | 2850.00 |
| CLARK | MANAGER | 10 | ACCOUNTING | 2450.00 |
+-------+---------+--------+------------+---------+
Test31
# 题意：列出所有员工的年工资，按年薪从低到高排序
select empno,ename,(sal+ifnull(comm,0))*12 as year_sal
from emp
order by year_sal asc;
+-------+--------+----------+
| empno | ename | year_sal |
+-------+--------+----------+
| 7369 | SMITH | 9600.00 |
| 7900 | JAMES | 11400.00 |
| 7876 | ADAMS | 13200.00 |
| 7934 | MILLER | 15600.00 |
| 7844 | TURNER | 18000.00 |
| 7521 | WARD | 21000.00 |
| 7499 | ALLEN | 22800.00 |
| 7782 | CLARK | 29400.00 |
| 7654 | MARTIN | 31800.00 |
| 7698 | BLAKE | 34200.00 |
| 7566 | JONES | 35700.00 |
| 7788 | SCOTT | 36000.00 |
| 7902 | FORD | 36000.00 |
| 7839 | KING | 60000.00 |
+-------+--------+----------+
Test32
# 题意：求出员工领导的薪水超过 3000 的员工名称与领导名称
select a.ename '员工',b.ename '领导',b.sal '领导的薪水'
from emp a
join emp b
on a.mgr = b.empno
where b.sal > 3000;
+-------+------+------------+
| 员工 | 领导 | 领导的薪水 |
+-------+------+------------+
| JONES | KING | 5000.00 |
| BLAKE | KING | 5000.00 |
| CLARK | KING | 5000.00 |
+-------+------+------------+
Test33
# 题意：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,ifnull(sum(e.sal),0) sum_sal,count(e.empno) emp_count
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 | sum_sal | emp_count |
+--------+------------+---------+----------+-----------+
| 20 | RESEARCH | DALLAS | 10875.00 | 5 |
| 30 | SALES | CHICAGO | 9400.00 | 6 |
| 40 | OPERATIONS | BOSTON | 0.00 | 0 |
+--------+------------+---------+----------+-----------+
Test34
# 题意：给任职日期超过 30 年的员工加薪 %10
第一步：查询认知日期超过 30 年的员工，并列出其涨薪后的薪资
select ename,timestampdiff(year,hiredate,now()) as work_year,sal*1.1 as up_sal
from emp
where timestampdiff(year,hiredate,now()) > 30;
+--------+-----------+---------+
| ename | work_year | up_sal |
+--------+-----------+---------+
| SMITH | 41 | 880.00 |
| ALLEN | 41 | 1760.00 |
| WARD | 41 | 1375.00 |
| JONES | 41 | 3272.50 |
| MARTIN | 40 | 1375.00 |
| BLAKE | 40 | 3135.00 |
| CLARK | 40 | 2695.00 |
| SCOTT | 35 | 3300.00 |
| KING | 40 | 5500.00 |
| TURNER | 40 | 1650.00 |
| ADAMS | 34 | 1210.00 |
| JAMES | 40 | 1045.00 |
| FORD | 40 | 3300.00 |
| MILLER | 40 | 1430.00 |
+--------+-----------+---------+
第二步：更新到表格中
update emp set sal = sal*1.1
where ifnull(timestampdiff(year,hiredate,now()),0) > 30;