mysql - 如何从多列中获取值的计数

Question

我有带有以下列的 users_details 表

martial_status | religion | education 

我想从下表中获取值的计数，如下所示。

married (100)
single (200)
Muslim(50)
Jews (50)
Christian(50)
Graduates(100) 
etc, etc. 

我不知道是否可以使用单个 SELECT 获得所有计数，请帮助。

Answer 1

它不完全是一个单一的SELECT语句，但您可以使用一个查询来检索它，如下所示（假设列是兼容的）：

( SELECT `martial_status`, COUNT(*) as `cnt` FROM user_details GROUP BY `martial_status` )
UNION
( SELECT `religion`, COUNT(*) as `cnt` FROM user_details GROUP BY `religion` )
UNION
( SELECT `education `, COUNT(*) as `cnt` FROM user_details GROUP BY `education` )

Answer 2

您需要分别处理每一列，然后合并它-

  SELECT martial_status, count(*)
  FROM USER_DETAILS
  GROUP BY martial_status
UNION ALL
  SELECT religion, count(*)
  FROM USER_DETAILS
  GROUP BY religion
UNION ALL
  SELECT education, count(*)
  FROM USER_DETAILS
  GROUP BY education

Answer 3

你可以这样做：

select sum(case when religion = 'Muslim'
           then 1
           else 0 
           end) as muslims,
       sum(case when martial_status = 'married'
           then 1
           else 0 
           end) as married
       ...
from your_table

一个较短的版本是：

select sum(religion = 'Muslim') as muslims,
       sum(martial_status = 'married') as married
       ...
from your_table

Answer 4

使用select没有子查询或类似查询的单个查询很棘手，但我相信单个查询也应该适合您。您可以通过一次选择来获取给定列的所有计数，然后使用它union all来合并结果，以便单个查询将为您获取所有列的所有计数。

select martial_status, count(*) from user_details group by martial_status
union all
select religion, count(*) from user_details group by religion
union all
select education, count(*) from user_details group by education

如果您NULL的表中有值，您可能希望从结果中省略这些值。

如果它确实是您需要的单个选择，那么您将不得不更改表格的布局，但我无法想象这种要求的正当理由。