mysql - 如何在 MySQL 中使用 case 语句

Question

我在使用 where 条件的 mysql 语句中使用三个查询，例如，如何将其作为单个查询

SELECT COUNT(*) as A FROM tbl_user WHERE (b=1 AND c=0)  AND (d=1 AND e=1)
SELECT COUNT(*) as M FROM tbl_user WHERE (H=1 AND I=0)  AND (J=1 AND K=1)

Answer 1

SELECT 
sum(case when (b=1 AND c=0)  AND (d=1 AND e=1) then 1 else 0 end) as CountA,
sum(case when (H=1 AND I=0)  AND (J=1 AND K=1) then 1 else 0 end) as CountM
 FROM tbl_user 

Answer 2

您不需要CASE声明来执行此操作（尽管它可能比使用IFif 条件包含ORs 更容易阅读），使用 s 可以更好地传达意图IF：

SELECT SUM(IF(b=1 AND c=0 AND d=1 AND e=1, 1, 0)) AS A,
       SUM(IF(H=1 AND I=0 AND J=1 AND K=1, 1, 0)) AS M
FROM tbl_user