MySQL 在一个查询中具有不同条件的两个 SELECTS答案

【问题标题】：MySQL two SELECTS with different conditions in one queryMySQL 在一个查询中具有不同条件的两个 SELECTS
【发布时间】：2017-05-12 07:40:30
【问题描述】：

我已经查看了其他类似性质的问题，但没有找到解决方案。

我有一个查询，在注册过程中获取男性的 SUM 数据，然后获取女性的 SUM 数据。它针对两个表中的相同数据，只是条件不同。这两者如何合二为一？

这是男性的查询：

SELECT 
    SUM(signup_data.submited) AS SubmitedMales,
    SUM(signup_data.approved) AS ApprovedMales,
FROM `signup_data`
    LEFT JOIN users ON signup_data.user_id = users.user_id
    WHERE users.sex = 'male'

女性查询：

SELECT 
    SUM(signup_data.submited) AS SubmitedFemales,
    SUM(signup_data.approved) AS ApprovedFemales,
FROM `signup_data`
    LEFT JOIN users ON signup_data.user_id = users.user_id
    WHERE users.sex = 'female'";

谢谢！

【问题讨论】：

这个怎么样：stackoverflow.com/questions/2309943/…

标签： mysql

【解决方案1】：

您应该使用条件SUM() 使用CASE 表达式，例如

SUM(case when users.sex = 'male' then signup_data.submited end) AS SubmitedMales,

您的查询应该是

SELECT 
    SUM(case when users.sex = 'male' then signup_data.submited end) AS SubmitedMales,
    SUM(case when users.sex = 'male' then signup_data.approved end) AS ApprovedMales,
    SUM(case when users.sex = 'female' then signup_data.submited end) AS SubmitedFemales,
    SUM(case when users.sex = 'female' then signup_data.approved end) AS ApprovedFemales,
FROM `signup_data`
    LEFT JOIN users ON signup_data.user_id = users.user_id

【讨论】：

非常感谢！非常有帮助！ :)

【解决方案2】：

您可以在聚合函数中使用case 来使用条件聚合：

SELECT 
    SUM(case when users.sex = 'female' then signup_data.submited else 0 end) AS SubmitedFemales,
    SUM(case when users.sex = 'female' then signup_data.approved else 0 end) AS ApprovedFemales,
    SUM(case when users.sex = 'male' then signup_data.submited else 0 end) AS SubmitedMales,
    SUM(case when users.sex = 'male' then signup_data.approved else 0 end) AS ApprovedMales
FROM `signup_data`
    LEFT JOIN users ON signup_data.user_id = users.user_id;

【讨论】：

【解决方案3】：

SELECT * FROM

(SELECT 
    SUM(signup_data.submited) AS SubmitedMales,
    SUM(signup_data.approved) AS ApprovedMales,
FROM `signup_data`
    LEFT JOIN users ON signup_data.user_id = users.user_id
    WHERE users.sex = 'male') AS T1

(SELECT 
    SUM(signup_data.submited) AS SubmitedFemales,
    SUM(signup_data.approved) AS ApprovedFemales,
FROM `signup_data`
    LEFT JOIN users ON signup_data.user_id = users.user_id
    WHERE users.sex = 'female') AS T2

【讨论】：