MySQL的慢COUNT（）

Question

我有一個查詢的一些困難：

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，我試圖讓每個類別總downloadcount但此查詢每次我運行它時掛起。

下載表有+ - 20000行

我在做什麼錯？

Answer 1

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

Answer 2

我想你會更好，這樣做：（d *）

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