如何使用case語句在MySQL

Question

我正在使用三個查詢在mysql的語句中使用WHERE條件 例如，如何使這個作爲一個單一的查詢

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

你並不需要一個CASE語句來做到這一點（雖然它可能會在一定程度上更容易比使用IF如果條件包含OR s到讀），其目的是與IF更好的輸送：

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 

Answer 2

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