mysql - 是否可以在同一个查询中计算两列

Question

假设我有以下表结构:

t1
-------------
id // row id
userID_follower // this user is a follows another member
userID_following  // other member that this user 

是否可以运行单个查询来结合以下两者:

1. 此人关注了多少用户

   select COUNT(id) from t1 WHERE userID_follower = ".$myID." ."

2. 有多少用户关注此人

   select COUNT(id) from t1 WHERE userID_following = ".$myID."

谢谢。

Answer 1

在 MySql 中，您可以在条件上使用 SUM() 函数，因为假条件将等于 0，而真条件将等于 1:

SELECT SUM(userID_follower = $myID) AS followerCount,
   SUM(userID_following = $myID) AS followingCount
FROM t1
WHERE userID_follower = $myID
   OR userID_following = $myID