mysql - 如何按组分隔两列计数？

Question

当我这样做时，

SELECT id, gender, count(1)
FROM class_student
WHERE id = 1
GROUP BY gender

我明白了

id  gender    count
--------------------
1   female    10
1   male      5  

我怎样才能得到这个？

id female male
---------------
1  10     5

下面的查询是执行此操作的正确方法吗？

SELECT
    id,
    (select count(1) from class_student
     where id = 1 AND gender='female') AS female,
    (select count(1) from class_student
     where id = 1 AND gender='male') AS male
FROM class_student
GROUP BY id

Answer 1

你可以使用大小写选择

  SELECT id
         , sum(case when gender = 'male' then 1 else 0 end) male, 
         , sum(case when gender = 'female' then 1 else 0 end) female
    FROM class_student
    WHERE id = 1
    GROUP BY id