性能问题 - 重构执行相同连接的选择子查询

Question

在 MySQL 中，您将如何重新编写一个 SELECT 查询，其中 JOIN SELECT 子查询执行几乎相同的操作。

就我而言，我遇到了性能问题，因为在子查询中，我需要为每个子查询加入相同的表，这是一项繁重的操作。

考虑下面的（丑陋的）例子：

set @businessdate = '2020-01-24';

Select Daily.*, Monthly.Price, Yearly.Price FROM
# DAILY
(Select @businessdate as BusinessDate, t1.Owner , SUM(t.Price) AS DailyPrice
FROM Table t
INNER JOIN Table2 t2 on ...
INNER JOIN Table1 t1 on ...
where t2.date = @businessdate
GROUP BY t1.Owner) Daily

INNER JOIN
# MONTHLY
(Select SUM(t.Price) AS Price, t1.Owner
FROM Table t
INNER JOIN Table2 t2 on ...
INNER JOIN Table1 t1 on ...
where MONTH(t2.date) = MONTH(@businessdate) and YEAR(t2.date) = YEAR(@businessdate)
GROUP BY t1.Owner) Monthly

INNER JOIN
#YEARLY
(Select SUM(t.Price) AS Price, t1.Owner
FROM Table t
INNER JOIN Table2 t2 on ...
INNER JOIN Table1 t1 on ...
where YEAR(t2.date) = YEAR(@businessdate)
GROUP BY t1.Owner) Yearly

原因是我需要 where 子句中的日期（来自 t2），以及来自 t1 的组中的一个字段。我还需要显示 t1 中的一些字段。

我只需要SUM(Price)（每月和每年的价格......）所以对我来说，即使它工作正常（非常慢......）子查询中的连接听起来也有点过头了（非常慢......）

Answer 1

您可以对单个查询使用条件聚合：

Select
    @businessdate as BusinessDate, ... ,
    SUM(CASE WHEN t2.date = @businessdate THEN t.Price ELSE 0 END) AS DailyPrice,
    SUM(CASE WHEN MONTH(t2.date) = MONTH(@businessdate) AND
                  YEAR(t2.date) = YEAR(@businessdate)
             THEN t.Price ELSE 0 END) AS MonthlyPrice,
    SUM(CASE WHEN YEAR(t2.date) = YEAR(@businessdate)
             THEN t.Price ELSE 0 END) AS AnnualPrice
FROM Table t
INNER JOIN Table2 t2 on ...
INNER JOIN Table1 t1 on ...
GROUP BY t1.Owner

这至少可以让您避免不必要的通过连接的表。请注意，您的 GROUP BY 子句在书面上无效；除条件总和外，营业日期是唯一可以选择的有效单列。