mysql优化与子查询的左连接

Question

我担心性能。

可以优化以下mysql查询吗？

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。性能几乎取决于带有group by子句的两个子查询的性能。

让我们看一看其中的一些改进。

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status值不等于1的行很多，并且具有复合索引，则重写查询将更快。

专业提示：日期时间值的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 */