复杂的IF语句3个表(Complex IF statement with 3 tables)

这是一个延续从昨天这个问题 。

这里是我的三个表：

战士表

fighter_id |  name
-----------------------
1          | John
2          | Steve
3          | Bill
4          | Bobby

事件表

event_id  |  event_name  |  event_date
-------------------------------------------
1          | MMA         |  01/01/2010
2          | Cool        |  02/20/2010
3          | Yeaa!       |  04/15/2010

战斗表

fight_id  |  fighter_a  |  fighter_b  |  winner  |  method  |  event
-----------------------------------------------------------------------
1         | 1           |  2          |  1       | Sub      | 1
2         | 4           |  1          |  4       | KO       | 2
3         | 1           |  3          |  NULL    | Draw     | 3

结果试图让

result  |  opponent  |  method  |  event  |  date        
----------------------------------------------------------
Draw    | Bill       |  Draw    |  Yeaa!  |  04/15/2010  
Loss    | Bobby      |  KO      |  Cool   |  02/20/2010 
Win     | Steve      |  Sub     |  MMA    |  01/01/2010

所以在打架表，fighter_a，fighter_b和赢家是对应于战斗机表fighter_id整数。

我基本上是检索基于fighter_id（fighter_id $）数据的页面上。

我试图与战斗机，其中包括他的对手的名字，结果（赢，损失，画，或NC），方法，EVENT_NAME和EVENT_DATE的每次吵架创建行。 我们面临的挑战是，赢家可以在任fighter_a或fighter_b。 这并不总是在同一列。 我感谢所有帮助我能。

select 
    fight_id,
    CASE
      WHEN winner is not null and winner=fighter_id then 'win'
      WHEN winner is not null and winner<>fighter_id then 'loss'
      WHEN winner is null and method='Draw' then 'draw'
      WHEN winner is null and method = 'No Contest' then 'no contest'
      ELSE ''
    END as match_result,
    participant.name 'participant',
    opponent.name 'opponent'
FROM fights
    INNER JOIN fighters as participant on participant.fighter_id = fights.fighter_a
    INNER JOIN fighters as oppoent on opponent.fighter_id = fights.fighter_b
WHERE 
    fighter_a=$fighter_id OR fighter_b=$fighter_id
ORDER BY
    event_date DESC

Answer 1:

使用子查询的用条件来进行切换，你正在寻找一个在column_a，如果它在column_b的fighter_id，这样一来，它简化了您的操作，并在外部查询联接：

SELECT
    (
        CASE
            WHEN a.winner = a.f_a THEN 'Win'
            WHEN a.winner = a.f_b THEN 'Loss'
            WHEN a.winner IS NULL THEN a.method
        END
    ) AS result,
    b.name AS opponent,
    a.method AS method,
    c.event_name AS event,
    c.event_date AS date
FROM
    (
        SELECT 
            IF(fighter_b = $fighter_id, fighter_b, fighter_a) AS f_a,
            IF(fighter_b = $fighter_id, fighter_a, fighter_b) AS f_b,
            winner,
            method,
            event
        FROM 
            fights
        WHERE
            $fighter_id IN (fighter_a, fighter_b)
    ) a
INNER JOIN
    fighters b ON a.f_b = b.fighter_id
INNER JOIN
    events c ON a.event = c.event_id
ORDER BY
    c.event_date DESC

另外，如果获奖者字段为空，然后就呼应法领域。 这样一来，当你想去的地方的赢家是空到您的系统中添加另一种类型的方法，你不必让更多的条件检查会附上你的CASE语句。

Answer 2:

你可以使用一个联盟：

SELECT CASE WHEN winner = participant_id THEN 'Win'
            WHEN winner = opponent_id then 'Loss'
            ELSE method
       END AS result, fighters.name AS opponent, method, event_name, event_date
  FROM fights
  INNER JOIN fighters ON fighter_id = opponent_id
  INNER JOIN events ON event = event_id
  WHERE participant_id = $fighter_id
UNION ALL
SELECT CASE WHEN winner = participant_id THEN 'Loss'
            WHEN winner = opponent_id then 'Win'
            ELSE method
       END AS result, fighters.name AS opponent, method, event_name, event_date
  FROM fights
  INNER JOIN fighters ON fighter_id = participant_id
  INNER JOIN events ON event = event_id
  WHERE opponent_id = $fighter_id
ORDER BY event_date DESC

Answer 3:

你可以只修改你CASE语句，以配合$fighter_id 。

所以，你的CASE语句是-

select fight_id,
       CASE
           WHEN winner is not null and winner = f.fighter_id then 'win'
           WHEN winner is not null and winner <> f.fighter_id then 'loss'
           WHEN winner is null and method='Draw' then 'draw'
           WHEN winner is null and method = 'No Contest' then 'no contest'
           ELSE ''
        END as match_result,
        f.name AS participant,
        (SELECT o.name FROM fighters o WHERE o.fighter_id = IF(f.fighter_id = fs.fighter_a, fs.fighter_b, fs.fighter_a)) AS opponent
FROM fights fs,
     fighters f
WHERE f.fighter_id = $fighter_id
AND (fs.fighter_a = f.fighter_id OR fs.fighter_b = f.fighter_id)

Answer 4:

SELECT
    CASE
      WHEN winner is not null and winner=fighter_id then 'win'
      WHEN winner is not null and winner<>fighter_id then 'loss'
      WHEN winner is null and method='Draw' then 'draw'
      WHEN winner is null and method = 'No Contest' then 'no contest'
      ELSE ''
    END result,
    f2.name opponent,
    method,
    event_name event,
    event_date date
FROM fights f1
INNER JOIN fighters f2
ON f1.fighter_b = f2.fighter_id
INNER JOIN events e
ON e.event_id = f1.event
ORDER BY date DESC

文章来源: Complex IF statement with 3 tables