將同一張表兩次連接到不同的列

Question

我有一張桌子產品和一張桌子位置。 產品表具有兩列pickLocation和recLocation。 在位置表中，我有id和name列。 pickLocation和recLocation具有位置表中的ID。 我該如何在Codeigniter中加入表格。

這是我的代碼

$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");

這是產品表

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

這是位置表

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

我想要這樣的結果

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

Answer 1

使用別名。 另外，除了join子句外，您的產品表永遠不會出現。 它也應該在從。

$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"); 

Answer 2

您需要使用別名，以便能夠區分這兩個聯接。 嘗試這樣的事情：

$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");