Question

我担心性能。

是否可以优化以下mysql查询？

SELECT u.name, t2.transactions, o2.orders FROM users AS u

LEFT JOIN (
    SELECT t.aid AS tuid, SUM( IF( t.status = 1, t.amount, 0 ) ) AS transactions
    FROM transactions AS t 
    WHERE ( t.datetime BETWEEN ('2018-01-01 00:00:00') AND ( '2020-01-01 23:59:59' ) ) GROUP BY t.aid
) AS t2 ON tuid = u.id 

LEFT JOIN (
    SELECT o.aid AS ouid, SUM(o.net) AS orders FROM orders AS o 
    WHERE ( o.date BETWEEN ('2018-01-01 00:00:00') AND ( '2020-01-01 23:59:59' ) ) GROUP BY o.aid 
) AS o2 ON ouid = u.id

WHERE u.status = 1
ORDER BY t2.transactions DESC

基本上，我需要汇总来自多个表的用户数据（并能够对其进行排序）

Answer 1

查询中没有明显的查询性能反模式。性能在很大程度上取决于两个带有group by子句的子查询的性能。

让我们看一看其中的一些改进之处。

SELECT t.aid AS tuid, 
       SUM( IF( t.status = 1, t.amount, 0 ) ) AS transactions
  FROM afs_transactions AS t 
 WHERE t.datetime BETWEEN '2018-01-01 00:00:00' AND '2020-01-01 23:59:59'
 GROUP BY t.aid

如果您在afs_transactions.datetime上有索引，则可以。

但是整个子查询都可以重写

SELECT t.aid AS tuid, 
       SUM( t.amount ) AS transactions
  FROM afs_transactions AS t 
 WHERE t.datetime BETWEEN '2018-01-01 00:00:00' AND '2020-01-01 23:59:59'
   AND t.status = 1
 GROUP BY t.aid

此查询将利用(status, datetime)上的复合索引。如果您有许多行，其中status的值不等于1，并且具有复合索引，则重写的查询会更快。

专业提示：对于日期时间值，BETWEEN通常是一个糟糕的选择，因为59:59。尝试使用<而不是BETWEEN的<=作为范围的结尾。

 WHERE t.datetime >= '2018-01-01'
   AND t.datetime <  '2020-01-02'   /* notice, it's the day after the range */

Answer 2

多个JOIN ( SELECT ... )曾经是性能杀手（5.6之前的版本）。现在，它可能是一个性能问题。

替代方法是

SELECT u.name,
       ( SELECT ... WHERE ...=u.id ) AS transactions,
       ( SELECT ... WHERE ...=u.id ) AS orders
    FROM users AS u
    WHERE  u.status = 1
    ORDER BY  transactions DESC

第一个子查询是一个相关子查询，看起来像

       ( SELECT SUM( IF(status = 1, amount, 0)
            FROM  transactions
            WHERE  aid = u.id
              AND  datetime >= '2018-01-01'
              AND  datetime  < '2018-01-01' + INTERVAL 2 YEAR`
       ) AS transactions

（另一个相似。）

索引：

users:         INDEX(status, name, id)   -- "covering"
transactions:  INDEX(aid, datetime)
orders:        INDEX(aid, date)  or  INDEX(aid, date, net)

MySQL优化与子查询左联接

2 个答案: