为不同的列加入相同的 table 两次

Question

我有一个 table 个产品和一个 table 个位置。 products table 有两列 pickLocation 和 recLocation。在位置 table 我有 id 和 name 列。 pickLocation 和 recLocation 的 id 来自位置 table。我怎样才能在 codeigniter 中加入 table。

这是我的代码

$this->db->select("locations.name as plname");
$this->db->select("locations.name as rcname");
$this->db->join("locations","locations.id=products.pickLocation","LEFT");
$this->db->join("locations","locations.id=products.recLocation","LEFT");

这是产品 table

+----+--------------+-------------+
| Id | pickLocation | recLocation |
+----+--------------+-------------+
|  1 |           12 |          23 |
|  2 |           12 |          12 |
+----+--------------+-------------+

这是位置table

+----+-----------+--+
| Id |   name    |  |
+----+-----------+--+
| 12 | Location1 |  |
| 23 | Location2 |  |
+----+-----------+--+

我想要这样的结果

+-----------------------+
| 1 Location1 Location2 |
+-----------------------+
| 2 Location1 Location1 |
+-----------------------+

Answer 1

您需要使用别名，以便能够区分这两个联接。尝试这样的事情：

$this->db->select("pickLoc.name as plname");
$this->db->select("recLoc.name as rcname");
$this->db->join("locations as pickLoc","pickLoc.id=products.pickLocation","LEFT");
$this->db->join("locations as recLoc","recLoc.id=products.recLocation","LEFT");

Answer 2

使用别名。此外，您的产品 table 绝不会出现在连接子句中。它也应该在from.

$query = $this->db->select("p.id, l1.name as plname, l2.name as rcname")
                 ->join("location l1", "l1.id = p.pickLocation", "left")
                 ->join("location l2", "l2.id = p.recLocation", "left")
                 ->get("product p");

为不同的列加入相同的 table 两次

joining the same table twice for different columns

php

mysql

join

codeigniter