SELECT其中column1 = column2

Question

在過去的幾個小時里，我一直在努力實現以下目標：

$stmt = $db->query( "SELECT league_match_id as match_id, league_match_home_team as home_team, league_match_away_team as away_team FROM $table WHERE (( home_team = away_team ) AND (away_team = home_team))" );

假設我們有team1和team2。 在Team1在家並且Team2不在的情況下進行比賽。 存儲另一個比賽（行），其中team2是主隊，而team1不在。 我想通過一個查詢選擇兩個團隊。

沒有團隊在玩自己，我試圖獲得2行，其中home_team和away_team的值被鏡像。

有人可以幫助我嗎？

*更新*

我得到的回報如下：

Array
(
   [0] => Array
    (
        [t1_id] => 26
        [t1_home] => 2
        [t1_away] => 1
        [t2_id] => 24
        [t2_home] => 1
        [t2_away] => 2
    )

   [1] => Array
    (
        [t1_id] => 28
        [t1_home] => 3
        [t1_away] => 1
        [t2_id] => 25
        [t2_home] => 1
        [t2_away] => 3
    )

   [2] => Array
    (
        [t1_id] => 24
        [t1_home] => 1
        [t1_away] => 2
        [t2_id] => 26
        [t2_home] => 2
        [t2_away] => 1
    )

   [3] => Array
    (
        [t1_id] => 29
        [t1_home] => 3
        [t1_away] => 2
        [t2_id] => 27
        [t2_home] => 2
        [t2_away] => 3
    )

   [4] => Array
    (
        [t1_id] => 25
        [t1_home] => 1
        [t1_away] => 3
        [t2_id] => 28
        [t2_home] => 3
        [t2_away] => 1
    )

   [5] => Array
    (
        [t1_id] => 27
        [t1_home] => 2
        [t1_away] => 3
        [t2_id] => 29
        [t2_home] => 3
        [t2_away] => 2
    )

)

如果Array [0]和Array [2]相同，則它們只是鏡像。 我可以擺脫這里的重復嗎？ 我希望只有Array [0]或Array [2]。 這可能嗎？

Answer 1

SELECT 
   t1.league_match_id , 
   t1.league_match_home_team , 
   t1.league_match_away_team ,
   t2.league_match_id , 
   t2.league_match_home_team, 
   t2.league_match_away_team   
FROM 
   {$table} t1 JOIN {$table} t2 ON t1.league_match_home_team=t2.league_match_away_team as away_team  AND 
                                   t2.league_match_home_team=t1.league_match_away_team as away_team
 GROUP BY
   t1.league_match_id , 
   t1.league_match_home_team , 
   t1.league_match_away_team ,
   t2.league_match_id , 
   t2.league_match_home_team, 
   t2.league_match_away_team 

Answer 2

我懷疑“主隊”與“客隊”是否會存在任何相同的行。

聽起來好像要查找匹配的兩行。

根據查詢中的條件，聽起來您可能想要這樣的東西：

SELECT t1.league_match_id         AS t1_match_id
     , t1.league_match_home_team  AS t1_home_team
     , t1.league_match_away_team  AS t1_away_team
     , t2.league_match_id         AS t2_match_id
     , t2.league_match_home_team  AS t2_home_team
     , t2.league_match_away_team  AS t2_away_team
  FROM $table t1
  JOIN $table t2
    ON t1.league_match_home_team = t2.league_match_away_team
   AND t1.league_match_away_team = t2.league_match_home_team

假設您在表中有相應的行，例如

 id  home   away
 --  -----  ------
  2  bears  tigers
  3  tigers bears

如果有多個具有相同（家，客場）的行，則將獲得多個匹配項。 例如，使用：

 id  home   away
 --  -----  ------
  2  bears  tigers
  3  tigers bears
  5  tigers bears
  7  tigers bears
 11  bears  tigers

您總共將獲得十二行。 （ID值為2和11的行將分別與ID值為3、5和7的行“匹配”。）

---

UPDATE

消除重復項取決於重復項的來源。 添加DISTINCT關鍵字將確保結果集中沒有任何兩行完全相同，但是我懷疑您的重復問題比那更深。。。在多次聯賽中， bears和tigers在本國和tigers面對對方。

在這種情況下，您需要在表中添加一些其他內容，並需要一些謂詞來限制匹配項。 這可能是日期，並且是獲取“最新日期”的某種方法，但這取決於表中的其他內容。

僅顯示了各列，即可使用GROUP BY和諸如MAX()類的聚合函數為每個“匹配項”獲得一個不同的行。

例如：

SELECT MAX(t1.league_match_id)    AS t1_match_id
     , t1.league_match_home_team  AS t1_home_team
     , t1.league_match_away_team  AS t1_away_team
     , MAX(t2.league_match_id)    AS t2_match_id
     , t1.league_match_away_team  AS t2_home_team
     , t1.league_match_home_team  AS t2_away_team
  FROM $table t1
  JOIN $table t2
    ON t1.league_match_home_team = t2.league_match_away_team
   AND t1.league_match_away_team = t2.league_match_home_team
 GROUP 
    BY t1.league_match_home_team
     , t1.league_match_away_team

需要注意的是返回home ，並away從T2是多余的，因為t1.home = t2.away等從值t1和t2是相同的，不同之處在於home和away被交換。

要限制“反”行，這樣您將獲得(bears,tigers)但不會獲得(tigers,bears) ，您可以指定一個附加謂詞，以便僅獲得反面的“一側”：

AND t1.league_match_home_team < t2.league_match_home_team

---

跟進

（我的查詢中有一個拼寫錯誤，第一個JOIN謂詞應在右側指定t2. 。我相信OP找到了該問題並已解決。）

基於最新更新，要消除結果集中的“鏡像”反行，您可以添加這樣的謂詞（如果查詢有一個，則遵循GROUP BY子句。）

  HAVING t1_id < t2_id

（與WHERE子句不同， HAVING子句可以引用分配給返回列的別名。）

如果查詢中沒有GROUP BY ，則使用WHERE子句可能會獲得更好的性能：

WHERE t1.match_id < t2.match_id

如果獲得的兩行中的哪一條都不重要，則小於還是大於比較都無關緊要。 選擇要比較的t1和t2列中的哪一個（“ id”，“ home”或“ away”）都沒有關系，所需要做的只是保證t1和t2之間的列比較不同（所以您只會得到鏡子的一側。）