計數2列

Question

我有這樣的數據集：

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 

上給予uid我要計算有多少用戶在下面，多少後跟（給定用戶）。

結果集將是：

following  followers 
2    3 

這裏是做工作的查詢：

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

現在的問題是，In't有任何其他方式來完成這件事？或者它是實現這一目標的最佳方式？

Answer 1

如果您對uid和follows_uid單獨的索引，那麼我相信像你一樣使用子查詢是最快的方法來檢索單獨計數，因爲每個查詢將採取指數的優勢，檢索伯爵。

Answer 2

這是實現它的另一種方法。

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，要回答你的問題，你的子查詢方法實際上是實現它的最好方法。正如@FuzzyTree指出的，你可以使用索引來優化你的性能。

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