MySQL GROUP BY来自不同表的多个列 [英] MySQL GROUP BY multiple columns from different tables

问题描述

我有以下表格布局:

Table Data
+----------+-------------------------+
| Field    | Type                    |
+----------+-------------------------+
| type     | enum('type_b','type_a') |
| type_id  | int(11) unsigned        |
| data     | bigint(20) unsigned     |
+----------+-------------------------+

Table A and B:

+--------------+------------------+
| Field        | Type             |
+--------------+------------------+
| id           | int(11) unsigned |
| customer_id  | int(11) unsigned |
| ...                             |
+--------------+------------------+

在表数据中，有某些类型(a或b)的计量数据. 现在，我要永远向客户提供两种类型的数据a和b的总和.

In table Data there is some messurement data from a certain type (a or b). Now I want for ever customer the total sum for both types of data a and b.

所以，我想:选择总和，加入a或b并按a.customer_id，b.customer_id分组.

So, I thought: select the sum, join on a or b and group by a.customer_id, b.customer_id.

产生以下查询:

SELECT sum(d.data) as total
FROM data d, ta, tb
WHERE
(d.type LIKE "type_a" AND d.type_id = ta.id) 
OR 
(d.type LIKE "type_b" AND d.type_id = tb.id) 
GROUP BY ta.customer_id, tb.customer_id;

这不能给我正确的结果...

This doesn't get me the proper results...

我尝试了几种方法，左联接，在customer表上联接，并按customer.id分组等.有人知道我在做什么错吗?

I tried several approaches, left joins, joining on the customer table and group by customer.id etc. Does anyone have a clue what I'm doing wrong?

感谢！

推荐答案

您的查询

SELECT sum(d.data) as total
FROM data d, ta, tb
WHERE
(d.type LIKE "type_a" AND d.type_id = ta.id) 
OR 
(d.type LIKE "type_b" AND d.type_id = tb.id) 
GROUP BY a.customer_id, b.customer_id;

让我们说d中只有一条记录，它是type_a. ta和tb中分别有两个记录. d中的记录与d.type_id=ta.id上ta中的记录之一匹配.因此，(d x ta)的组合允许任何tb记录保留在最终结果中.您会得到意想不到的笛卡尔积.

Let's say there is only one record in d, and it is type_a. There are two records in ta and tb each. The record in d matches one of the records in ta on d.type_id=ta.id. Therefore, that combination of (d x ta) allows ANY tb record to remain in the final result. You get an unintended cartesian product.

SELECT x.customer_id, SUM(data) total
FROM
(
    SELECT ta.customer_id, d.data
    FROM data d JOIN ta
       ON (d.type LIKE "type_a" AND d.type_id = ta.id) 
    UNION ALL
    SELECT tb.customer_id, d.data
    FROM data d JOIN tb
       ON (d.type LIKE "type_b" AND d.type_id = tb.id) 
) X
GROUP BY x.customer_id;

这篇关于MySQL GROUP BY来自不同表的多个列的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！