在多行上使用 LEFT JOIN 简化我的 SQL

Question

我现在对 MySQL 和高效查询相当有经验，但仍然运行遇到问题...

我有两个 table，"invoices" 和 "salesRecords" 发票 table 包含发票的基本概述，销售记录按以下方式细分特定信息行关于购买的物品的行。

为简单起见，我们假设 table 如下所示：

发票

id    |   repairCharge     |    shippingCharge      |     total
 1    |       28.95        |         0              |     30.45   
 2    |       10.00        |         8.50           |     29.50

//注意；总计列包括销售记录中显示的项目

销售记录

invNo  |    itemNo   |  price    |   quantity   | discount  |   
  1    |     123     |  1.50     |      1       |     0     |  
  2    |     121     |  6.50     |      1       |     1.5   |  
  2    |     128     |  5.50     |      1       |     0     |

我想获取一个日期段内售出商品的总价值、人工费和运费，所以我需要：

对 Invoices 中的所有行求和 Table
JOIN（左？）SalesRecords Table ON invNo and SUM ((price-discount)*quantity)
为日期期间使用 WHERE 子句

我马上写这个SQL:

SELECT SUM((sr.price-sr.discount)*sr.quantity) as income,   
   SUM(i.repairCharge) as labour,
   SUM(i.shippingCharge) as carriage 
FROM invoices i 
    LEFT JOIN salesRecords sr ON sr.invNo=i.id
WHERE i.dateTime BETWEEN 1431647999 AND 1434360348`

这是错误的

因为，对于具有多个项目行的任何发票，我得到两个 table 的多个实例，因此 repairCharge 和 shippingCharge 值加倍或加倍等取决于该发票上购买了多少产品线。

所以，我四处乱逛并想出了一个解决方案...但它非常丑陋并且可能效率低下：

SELECT SUM(income) as income,
       SUM(labour) as labour,
       SUM(carriage) as carriage 
FROM (SELECT (SELECT SUM((price-discount)*quantity)
              FROM salesRecords
              where invno=i.id
              GROUP BY invNo) as income, 
             SUM(i.repairCharge) as labour,
             SUM(i.shippingCharge) as carriage 
      FROM invoices i 
      WHERE i.dateTime BETWEEN 1434326474 AND 1434361694
      GROUP BY id
     ) totals

任何人都可以建议简化并提高效率的最佳方法吗？

Answer 1

试试这个：

select sum(labour) as labour,
       sum(carriage) as carriage,
       sum(income) as income
from( select sum(i.repairCharge) as labour,
             sum(i.shippingCharge) as carriage,
             coalesce(sum((sr.price - sr.discount) * sr.quantity), 0) as income
      from Invoices i
      left join SalesRecords sr on i.id = sr.invNo
      group by i.id)t

Answer 2

就大多数其他 DBMS 的易读性和性能而言，我个人只会在子查询中汇总销售记录：

SELECT  SUM(COALESCE(sr.Income, 0)) AS Income,
        SUM(i.repairCharge) AS Labour,
        SUM(i.shippingCharge) AS Carriage
FROM    Invoices AS i
        LEFT JOIN
        (   SELECT  InvNo, SUM((price-discount)*quantity) AS Income
            FROM    SalesRecords
            GROUP BY InvNo
        ) AS sr
            ON sr.InvNo = i.ID
WHERE   i.dateTime BETWEEN 1434326474 AND 1434361694;

MySQL 在子查询上使用中间具体化（据我所知），如果这样做可能会对上述查询产生不利影响，因为它会首先汇总 SalesRecords 中的所有记录并在对发票日期应用过滤器之前将结果存储在散列 table 中，因此您的工作版本，但使用 JOIN 而不是相关子查询可能会执行得更好：

SELECT  SUM(COALESCE(i.Income, 0)) AS Income,
        SUM(i.repairCharge) AS Labour,
        SUM(i.shippingCharge) AS Carriage
FROM    (   SELECT  i.ID,
                    i.repairCharge,
                    i.shippingCharge,
                    SUM((sr.price - sr.discount) * sr.quantity) AS Income
            FROM    Invoices AS i
                    LEFT JOIN SalesRecords AS sr
                        ON sr.InvNo = i.ID
            WHERE   i.dateTime BETWEEN 1434326474 AND 1434361694
            GROUP BY i.ID, i.repairCharge, i.ShippingCharge
        ) AS i;

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