mysql查询部门人数大于所有部门平均人数的部门

Posted 2023-05-07

查询部门人数大于所有部门平均人数的部门编号，部门名称，部门人数
SELECT e.deptno,d.dename,count(empno) from emp e,dept d
where e.deptno = d.deptno and count(empno) >
(SELECT avg(COUNT(EMPNO)) FROM emp GROUP BY DEPTNO)
执行报错，请问怎么修改
oracle 里面语句是正确的，但是mysql这么写报错，问题应该出现在 avg（count（empno））这边

错误在于avg（count（empno））这里其实是按部门计数、按部门求平均两步查询，不能在一次子查询里实现。
其实可以跳出avg(count(，直接用count总人数除count部门数来求平均：select count(distinct empno)/count(distinct deptno) 参考技术A select t1.*, t2.s
from emp_hiloo t1 join (select deptno, avg(salary) s from emp_hiloo group by deptno) t2
on t1.deptno=t2.deptno
where t1.salary>t2.s追问

我要查询的是部门人数大于所有部门平均人数的部门编号，部门名称（如 a部门6人，b部门4人，c部门5人，那么部门平均人数是5人，大于平均人数的部门就是a部门，所以最后查询结果应该是显示a部门的部门编号、部门名称、部门人数

刚刚忘记说谢谢！

本回答被提问者和网友采纳 参考技术B 其一第一排count（empno）改为count(e.empno)
其二外层查询需要分组，不然你用count（*）就是错的
SELECT D.DEPTNO,D.DNAME,COUNT(E.ENAME)
FROM EMP E JOIN DEPT D ON E.DEPTNO=D.DEPTNO
GROUP BY D.DEPTNO,D.DNAME
HAVING COUNT(E.ENAME)>(
SELECT AVG(COUNT(ENAME)) FROM EMP GROUP BY DEPTNO
)

MySQL之多表查询练习

author_id	author_name
1	Kimmy
2	Abel
3	Bill
4	Berton

	bo ok_id	author_id	start_date	end_date
	9	1	2017-09-25 21:16:04	2017-09-25 21:16:06
	10	3
	11	2	2017-09-25 21:21:46	2017-09-25 21:21:47
	12	1
	13	8

 

	order_id	book_id	price	order_date
	1	9	0.2	2017-09-24 21:21:46
	2	9	0.6	2017-09-25 21:16:04
	3	11	0.1	2017-09-25 21:21:46

 

 

 

在以上表中执行ABC表关联

SELECT `authors`.*, `books`.book_id, `orders`.order_id, `orders`.price FROM `authors`
LEFT JOIN `books` ON `authors`.author_id = `books`.author_id
LEFT JOIN `orders` ON `books`.book_id = `orders`.book_id　　　　　　　　

#通过group by 分类，使用sum ,avg,count等函数求值

SELECT `authors`.*, sum(`orders`.price) FROM `authors`
LEFT JOIN `books` ON `authors`.author_id = `books`.author_id
LEFT JOIN `orders` ON `books`.book_id = `orders`.book_id
GROUP BY `books`.book_id

 

#使用where条件，where不能用于选取列的AS别名判断，MYSQL的处理机制是先进行选取，再进行筛选

SELECT `authors`.*, `books`.book_id, `orders`.order_id, sum(`orders`.price) AS prices FROM `authors`
LEFT JOIN `books` ON `authors`.author_id = `books`.author_id
LEFT JOIN `orders` ON `books`.book_id = `orders`.book_id AND `orders`.order_date >= `books`.start_date AND `orders`.order_date <= `books`.end_date
WHERE `orders`.price is not NULL
GROUP BY `books`.book_id

 

使用having关键字，对于无法使用where字段的price进行统计

SELECT `authors`.*, `books`.book_id, sum(`orders`.price)AS prices FROM `authors`
LEFT JOIN `books` ON `authors`.author_id = `books`.author_id
LEFT JOIN `orders` ON `books`.book_id = `orders`.book_id
GROUP BY `books`.book_id
HAVING prices > 0.1