如何将一个表中另一个表具有多个ID的两个表联接在一起？

Question

I need to join two tables tableA and tableB , but the problem is that in tableB I have two IDs from tableA and I need to join them so I get both values. I would like to achieve it using Codeigniter's active record class. Here is a small demo:

tableA:
╔══════════╦════════════╗
║ video_id ║ video_name ║
╠══════════╬════════════╣
║        1 ║ short      ║
║        2 ║ long       ║
║        3 ║ black      ║
║        4 ║ white      ║
╚══════════╩════════════╝

tableB
╔═════════╦════════╦════════╗
║ pair_id ║ pair_a ║ pair_b ║
╠═════════╬════════╬════════╣
║       1 ║      1 ║      2 ║
║       2 ║      1 ║      4 ║
║       3 ║      4 ║      3 ║
║       4 ║      3 ║      2 ║
╚═════════╩════════╩════════╝

this doesn't work:

$this->db->select('*')
         ->from("tableA")
         ->join('tableB AS A', 'tableA.video_id = A.pair_a')
         ->select("tableA.video_name as VIDEO_A")

         ->join('tableB AS B', 'tableA.video_id = B.pair_b')
         ->select("tableA.video_name as VIDEO_B")

         ->get()
         ->result();

The final result needs to be something like this:

stdClass Object
(
    [0] => stdClass Object
        (
            [VIDEO_A] => short
            [VIDEO_B] => long
        )

    [1] => stdClass Object
        (
            [VIDEO_A] => short
            [VIDEO_B] => white
        )

    [2] => stdClass Object
        (
            [VIDEO_A] => white
            [VIDEO_B] => black
        )

    [3] => stdClass Object
        (
            [VIDEO_A] => black
            [VIDEO_B] => long
        )

)

Answer 1

You mix up tableA and tableB in your query. For each item in B you want something, so start joining there. Then, join renamed table, and select the items from the renamed tables.

->from("tableB")
->join('tableA AS pairA', 'pairA.video_id = tableB.pair_a')
->join('tableA AS pairB', 'pairB.video_id = tableB.pair_b')
->select("pairA.video_name as VIDEO_A, pairB.video_name as VIDEO_B")