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mysql - 来自同一基础表的两个 GROUP BY 子查询的列总和

问题描述

更新 我确定了一种更简洁和计算最佳的方式来表达这个陈述。没有子查询没有多个连接。：

SELECT
month(hire_date) as month, 
sum(case when gender ="m" then 1 end) as male,
sum(case when gender ="f" then 1 end) as female,
count(*) as total 
FROM employees
GROUP BY MONTH(hire_date)

使用 MySQL员工示例数据库，我通过子查询两次查询同一个员工表并交叉连接结果以获取下面的数据透视表。我希望创建一个最终列，它是mcount和fcount

Month,Gender,mcount,gender,fcount
'1','M','14310','F','9549'
'2','M','14659','F','9789'
'3','M','16200','F','10717'
'4','M','15363','F','10190'
'5','M','15545','F','10398'
'6','M','15000','F','10003'
'7','M','15260','F','10345'
'8','M','15250','F','10146'
'9','M','14632','F','9684'

我曾尝试再次使用子查询来创建此列，但很明显我的两个 GROUP BY 子查询是构建此数据透视表的错误方法。

SELECT mbm.month, mbm.gender, mbm.count as mcount, fbm.gender, fbm.count as fcount
FROM
(SELECT MONTH(hire_date) as Month, gender, COUNT(*) as count
FROM employees
WHERE gender = "M"
GROUP BY gender,MONTH(hire_date)
) as mbm

CROSS JOIN (SELECT MONTH(hire_date) as Month, gender, COUNT(*) as count
FROM employees
WHERE gender = "F"
GROUP BY gender,MONTH(hire_date)
) AS fbm on mbm.Month = fbm.Month

标签： mysqlsql

解决方案

表达此陈述的一种更加简洁和计算优化的方式。没有子查询，没有多重连接，并且易于阅读：

SELECT
month(hire_date) as month, 
sum(case when gender ="m" then 1 end) as male,
sum(case when gender ="f" then 1 end) as female,
count(*) as total 
FROM employees
GROUP BY MONTH(hire_date)

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