计数2列

Question

我有这样的数据集：

id uid follows_uid status  
1 1  2   ACTIVE 
2 1  3   ACTIVE 
3 3  1   ACTIVE 
4 4  1   ACTIVE 
5 2  1   ACTIVE 

上给予uid我要计算有多少用户在下面，多少后跟（给定用户）。

结果集将是：

following  followers 
2    3 

这里是做工作的查询：

SELECT COUNT(*) as following, 
    (SELECT COUNT(*) FROM user_followers where follows_uid = 1 ) as followers 
FROM user_followers 
WHERE uid = 1 and `status` = 'ACTIVE' 

现在的问题是，In't有任何其他方式来完成这件事？或者它是实现这一目标的最佳方式？

Answer 1

如果您对uid和follows_uid单独的索引，那么我相信像你一样使用子查询是最快的方法来检索单独计数，因为每个查询将采取指数的优势，检索伯爵。

Answer 2

这是实现它的另一种方法。

select following.*, followers.* from 
(select count(uid) from user_followers where uid = 1) following, 
(select count(follows_uid) from user_followers where follows_uid = 1) followers; 

而且，要回答你的问题，你的子查询方法实际上是实现它的最好方法。正如@FuzzyTree指出的，你可以使用索引来优化你的性能。

Answer 3

SELECT 
    IFNULL(SUM(IF(uid = 1, 1, 0)), 0) as following, 
    IFNULL(SUM(IF(follows_uid = 1, 1, 0)), 0) as followers 
FROM user_followers 
WHERE (uid = 1 OR follows_uid = 1) 
AND `status` = 'ACTIVE'; 

Click here to see SQL Fiddle