MySQL的慢COUNT（）

Question

我有一个查询的一些困难：

SELECT d.*, 
     (SELECT COUNT(id) FROM downloads WHERE category = d.category) AS count 
FROM downloads d 
GROUP BY d.category 
ORDER BY count DESC 

所以，我试图让每个类别总downloadcount但此查询每次我运行它时挂起。

下载表有+ - 20000行

我在做什么错？

Answer 1

SELECT category, count(id) as count 
FROM downloads d 
GROUP BY d.category 
ORDER BY count DESC 

Answer 2

我想你会更好，这样做：（d *）

SELECT category, count(*) as cnt 
    FROM downloads 
GROUP BY category 
ORDER BY cnt desc;