Question

SELECT *, SUM(real_premier_num) AS real_premier_num, SUM(premier_num) AS premier_num, 
GROUP_CONCAT(tg_time SEPARATOR '-') AS post_time, GROUP_CONCAT(low_price SEPARATOR '-') 
AS low_price FROM `port_wbinfo` WHERE `city_id` = 12 AND `is_tg` = 0 GROUP BY
`hz_post_id` ORDER BY `off_time` DESC, `shelf_time` DESC, `id` DESC LIMIT 10

我创建了一个如下所示的索引，但它不起作用，我必须分组。

alter table port_wbinfo add index `city_tg` (`city_id`,`is_tg`);

Answer 1

您应该将查询编写为：

SELECT hz_post_id, SUM(real_premier_num) AS real_premier_num,
       SUM(premier_num) AS premier_num,
       GROUP_CONCAT(tg_time SEPARATOR '-') AS post_time, 
       GROUP_CONCAT(low_price SEPARATOR '-') AS low_price
FROM port_info pi
WHERE city_id = 12
GROUP BY hz_post_id
ORDER BY MAX(id) DESC;

带有SELECT *的

GROUP BY没有意义。最新版本的MySQL - 与几乎所有其他数据库一样 - 会发出错误（使用默认设置）。

对于此查询，您可以在port_info(city_id, hz_post_id)上使用索引。如果您愿意，可以将real_premier_num, premier_num, tg_time, low_price, id添加到索引中，以便涵盖查询。

这可能不会产生重大改进，但覆盖指数可能有所帮助。

我下面有一个sql，我不知道如何优化？

1 个答案: