MySQL 分组统计查询 表连接（3）

1 查询底薪超过公司平均底薪的员工信息？

select
e.empno,e.ename,e.sal
from t_emp as e
join (select avg(sal) as avg from t_emp) t on e.sal > t.avg

2 统计人数 格式化时间

select
count(*) as count, max(a.sal),min(a.sal),
avg(a.sal) , floor(avg(DATEDIFF(NOW(),a.hiredate)/365))
from
t_emp a
join t_dept b on a.deptno = b.deptno
where
b. dname = 'RESEARCH'

3 查询每种职业的最高工资，最低工资 平均工资 ...

select
e.job,
max(e.sal + IFNULL(e.comm,0)),
min(e.sal + IFNULL(e.comm,0)),
avg(e.sal + IFNULL(e.comm,0)),
max(s.grade),
min(s.grade)
from t_emp e join t_salgrade s
on e.sal + IFNULL(e.comm,0) BETWEEN s.losal and s.hisal
GROUP BY e.job

4 查询每个底薪超过部门平均底薪的员工

select e.empno,
e.ename,
e.sal

from t_emp e join
(select deptno,AVG(sal) avg from t_emp GROUP BY deptno) t
on e.deptno = t.deptno
where
e.sal >= t.avg

5 统计部门名称和人数

select
d.dname,count(e.deptno)
from t_dept d
left join t_emp e on d.deptno = e.deptno
GROUP BY d.deptno HAVING d.dname is not null

6  union 连接使用方法

(select
d.dname,count(e.deptno)
from t_dept d
left join t_emp e on d.deptno = e.deptno
GROUP BY d.deptno)
union
(select
d.dname,count(*)
from t_dept d
right join t_emp e on d.deptno = e.deptno
GROUP BY d.deptno)

7 查询上司名称 编号

select
e.empno,
e.ename,
d.dname,
(e.sal+ IFNULL(comm,0)) AS sal,
s.grade,
FLOOR(DATEDIFF(NOW(),e.hiredate)/365) AS hire,
t.empno m_empno,
t.ename m_ename,
t.dname m_dname
from
t_emp e
left join t_dept d on d.deptno = e.deptno
left join t_salgrade s on e.sal BETWEEN s.losal and s.hisal
left join (select
e.deptno,e.empno,e.ename,d.dname
from t_emp e
join t_dept d on d.deptno = e.deptno) as t on t.empno = e.mgr