加入具有另一个表的两个公共列的 postgres 表

Posted 2023-02-16

【中文标题】加入具有另一个表的两个公共列的 postgres 表

【英文标题】：Join postgres table that has two common columns of another table

【发布时间】：2022-01-18 18:57:02

【问题描述】：

我有两张桌子：

Transactions:
+---------+--------------+------------+-----------+
| id      | address_from | address_to | value     |
+---------+--------------+------------+-----------+
| 1       |        1     |     2      | 1000      |
| 2       |        1     |     2      | 500       |
+---------+--------------+------------+-----------+

Addresses:
+---------+--------------+
| id      | address      |
+---------+--------------+
| 1       |   address1   |
| 2       |   address2   |
+---------+--------------+

我需要获取所有带有地址而不是 id 的交易：

SELECT * FROM transactions tr
JOIN addresses ad ON tr.address_from = ad.id OR tr.address_to = ad.id
WHERE tr.address_from = 1 OR tr.address_to = 1

然后我得到以下结果：

+---------+--------------+-----------+
| id      | address      | value     |
+---------+--------------+-----------+
| 1       |  address1    |   1000    |
| 1       |  address1    |   1000    | 
| 2       |  address2    |   500     |
| 2       |  address2    |   500     |
+---------+--------------+-----------+

但我需要这样的东西：

+---------+--------------+-------------+-----------+
| id      | address_from | address_to  | value     |
+---------+--------------+-------------+-----------+
| 1       |   address1   |   address2  | 1000      |
| 2       |   address1   |   address2  | 500       |
+---------+--------------+-------------+-----------+

我怎样才能得到这个结果？ 加入两列不是很贵吗？

【参考方案1】：

您可以尝试在同一张表上使用 2 个连接来获得预期的结果

SELECT tr.id,adf.address as address_from,adt.address as address_to,tr.value
    FROM transactions tr
JOIN addresses adf ON tr.address_from = adf.id
JOIN addresses adt ON tr.address_to = adt.id

【讨论】：

哦，我什至没有考虑过这种可能性。但是，大量的连接将如何影响具有数百万条记录的表呢？