Question

我无法弄清楚如何从第三个表中获取值，从第一个到第二个到第三个参考索引跳转。数据：

          Players
Player_ID| Player_Name| ...   
    1    | Adam Smith | ...  
    2    | John  Doe  | ...

              Participants
Participant_ID| Event_ID | Player_ID| ...  
      1       |     1    |     2    | ... 
      2       |     1    |     1    | ...

                              Games
Game_ID|Event_ID|White_player (patricipant id)|Black_Player (participant_id)| ...  
   1   |    1   |             1               |                 2           | ...

我基本上想要的是：

   Game_ID|Event_ID|White_player (patricipant id)|Black_Player (participant_id)| ...  
   1      |    1   |        John Doe             |            Adam Smith       | ...

但最后我需要像“John Doe vs Adam Smith”这样的字符串。我不想替换表中的值。我不知道我是否应该这样做，或者可能改变我的表结构。

Answer 1

允许多次加入同一个表。在这种情况下，您需要加入Players两次，以获取黑色和白色的名称。所以你需要这样的东西：

select g.game_id
       , wp.event_id
       , p1.player_name 
         || ' vs ' ||
         p2.player_name as competitors
from games g
     join participants wp
         on wp.event_id = g.game_id
         and wp.participant_id = g.white_player
     join players p1
         on wp.participant_id = p1.player_id
     join participants bp
         on bp.event_id = g.game_id
         and bp.participant_id = g.black_player
     join players p2
         on bp.participant_id = p2.player_id

Answer 2

经过一些修复，我得到了我想要的结果：

select p1.player_name || ' vs ' || p2.player_name as competitors, g.game_id
from games g
     join participants_list wp
         on wp.event_id = g.event_id
         and wp.participant_id = g.white_player
     join players p1
         on wp.player_id= p1.player_id
     join participants_list bp
         on bp.event_id = g.event_id
         and bp.participant_id = g.black_player
     join players p2
         on bp.player_id = p2.player_id

通过参考索引跳跃来接收价值

2 个答案: