Mysql 如何进行更快的最大n个组查询？

我正在使用此查询：

SELECT district, id
FROM adverts ls
GROUP BY district, id
HAVING (

SELECT count( * )
FROM adverts
WHERE district = ls.district
AND id > ls.id
) <5
ORDER BY district, id DESC ;

LIMIT 0 , 30

有没有办法加快速度？

试试这个：

SELECT    district, id, COUNT(b.district)
FROM      adverts a INNER JOIN adverts b
              ON a.district = b.district
WHERE     b.id > a.id
GROUP BY  district, id 
HAVING    COUNT(b.district) < 5
ORDER BY  district, id DESC 

选择地区、id、计数（b区）
从广告a内部连接广告b
在a区=b区
其中b.id>a.id
按地区分组，id
计数（b区）<5
按地区订购，id描述

根据定义，

连接

比

子查询

更快

试试这个：

SELECT    district, id, COUNT(b.district)
FROM      adverts a INNER JOIN adverts b
              ON a.district = b.district
WHERE     b.id > a.id
GROUP BY  district, id 
HAVING    COUNT(b.district) < 5
ORDER BY  district, id DESC 

选择地区、id、计数（b区）
从广告a内部连接广告b
在a区=b区
其中b.id>a.id
按地区分组，id
计数（b区）<5
按地区订购，id描述

根据定义，

连接

比

子查询

更快