MySQL - 查询中的复杂 SUM答案

【问题标题】：MySQL - Complicated SUMs inside QueryMySQL - 查询中的复杂 SUM
【发布时间】：2013-01-09 23:28:40
【问题描述】：

这很难解释。

我每天从tbl_customers 循环浏览我的客户记录数次。

SELECT c.* FROM tbl_customers c

我只返回客户的：customerid、name、phone、email

现在是奇怪的部分。我想在电子邮件之后再添加 3 列：totalpaid、totalowed、totalbalance 但是，这些列名在任何地方都不存在。

这是我如何查询每个：（作为单个查询）

SELECT SUM(total) AS totalpaid 
FROM tbl_customers_bills 
WHERE customerid = X
AND billtype = 1

SELECT SUM(total) AS totalowed 
FROM tbl_customers_bills 
WHERE customerid = X
AND billtype = 2

SELECT SUM(total) AS totalbalance 
FROM tbl_customers_bills 
WHERE customerid = X
AND billtype IN(1,2)

所以，billtype 是告诉我记录是否已支付的列。

我在这里不知所措。如何将 3 个单独的查询相加到第一个查询的循环中？

【问题讨论】：

标签： mysql sum subquery

【解决方案1】：

只需将客户加入账单并计算总和即可。要分离出totalpaid 和totalowed，您可以使用SUM(CASE 或SUM(IF 作为wless1's answer demonstrates

SELECT c.*,
        SUM(CASE WHEN billtype = 1 THEN total ELSE 0 END) totalpaid ,
        SUM(CASE WHEN billtype = 2 THEN total ELSE 0 END) totalowed ,
        SUM(total) AS totalbalance
FROM 
    tbl_customers c
    LEFT JOIN tbl_customers_bills  b
    ON c.customerid = b.customerid
     and billtype in (1,2)
GROUP BY 
     c.customerid

因为这是MySQL，所以只需要对客户的PK进行分组。

【讨论】：

【解决方案2】：

您可以使用GROUP、SUM 和IF 的组合来完成此操作

SELECT c.id, c.name, c.phone, c.email, 
SUM(IF(b.billtype = 1, b.total, 0)) AS totalpaid,
SUM(IF(b.billtype = 2, b.total, 0)) AS totalowed,
SUM(IF(b.billtype = 1 OR b.billtype = 2, b.total, 0)) AS totalbalance,
FROM tbl_customers c LEFT JOIN tbl_customers_bills b ON b.customerid = c.id
GROUP BY c.id

见： http://dev.mysql.com/doc/refman/5.0/en//group-by-functions.html http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html

【讨论】：