Question

这是三个表，order，order_record，pay，附近有2300000条记录。

在给1个order_id时，pay表中会有超过1条记录，所以我需要使用DISTINCT来删除重复的结果

现在我需要从order_id上的那三个表连接中获取不同的数据，下面是示例查询sql：

SELECT
    DISTINCT (a.order_id)
    a.order_id,a.user_id
    b.boss_order_id,
    c.pay_id,

    FROM order a
    LEFT JOIN order_record b ON a.order_id = b.order_id AND b.is_delete IN (0,1)
    LEFT JOIN pay c ON a.order_id = c.order_id AND c.is_delete =0  WHERE 1=1 AND a.is_delete IN (0,1)
    ORDER BY a.id DESC LIMIT 0, 10

此查询将花费大量时间。然后我改为使用“GROUP BY”：

SELECT

    a.order_id,a.user_id
    b.boss_order_id,
    c.pay_id,

    FROM order a
    LEFT JOIN order_record b ON a.order_id = b.order_id AND b.is_delete IN (0,1)
    LEFT JOIN pay c ON a.order_id = c.order_id AND c.is_delete =0  WHERE 1=1 AND a.is_delete IN (0,1)
    GROUP BY a.order_id
    ORDER BY a.id DESC LIMIT 0, 10

这次查询需要122秒。

有没有更快的实施方式？

Answer 1

您正在使用left join。因此，您可以这样做：

SELECT o.order_id, o.user_id, orr.boss_order_id, p.pay_id,
FROM (SELECT o.*
      FROM order o
      WHERE o.is_delete IN (0, 1)
      ORDER BY o.id DESC
      LIMIT 10
     ) o LEFT JOIN
     order_record orr
     ON o.order_id = orr.order_id AND
        orr.is_delete IN (0, 1) LEFT JOIN
     pay p
     ON o.order_id = p.order_id AND
        p.is_delete = 0 
WHERE 1=1 AND o.is_delete IN (0, 1)
GROUP BY o.order_id
ORDER BY o.id DESC
LIMIT 0, 10

您错误地使用了GROUP BY，因为您在SELECT中的非聚合列不在GROUP BY中。

Answer 2

另一种方法是让where子句完成大部分工作：

select ...
from order
left join order_using using (order_id)
...
where
order.order_id < (select max(order_id) from orders order by order_id limit 10) ...
limit 10

最终限制10很奇怪，但是如果您放弃该组，您可能会从订单中获得部分记录。即你可能想放弃它，并且只是放一个限价订单表。通过组，您将获得表b和c中的随机数据，除非您使用聚合函数告诉mysql您想要哪个行值。

来自3表的mysql“distinct query”对大数据执行缓慢

2 个答案: