选择其中 column1 = column2

Question

在过去的几个小时里，我一直在尝试完成以下任务，但没有任何运气：

$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))" );

假设我们有 team1 和 team2。在 Team1 在家而 Team2 不在的情况下进行比赛。另一场比赛（行）存储在 team2 在家而 team1 不在的地方。我想用一个查询选择两个团队。

没有球队在比赛，我试图获得 2 行，其中 home_team 和 away_team 的值是镜像的。

谁能帮我走上正轨？

* 更新 *

我得到的回报如下：

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，它们只是镜像。我可以摆脱这里的重复吗？我希望只有 Array[0] 或 Array[2]。这可能吗？

Answer 1

我怀疑是否会有“主队”与“客队”相同的行。

听起来好像您想找到 两个 匹配的行。

根据您查询中的条件，听起来您可能想要这样的东西：

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

这假设您在表中有相应的行，例如

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

如果有多行具有相同的 (home,away)，您将获得多个匹配项。例如，使用：

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

您将返回总共 12 行。 （id 值为 2 和 11 的行将分别与 id 值为 3、5 和 7 的行“匹配”。）

---

更新

消除重复取决于重复的来源。添加DISTINCT 关键字将确保结果集中没有两行完全相同，但我怀疑您的重复问题比这更深......bears 和tigers 彼此面对，家庭和客场，在多场联赛中。

在这种情况下，您需要在表格中添加一些额外的内容，以及一些谓词来限制匹配。这可能是日期，以及一些获取“最新日期”的方法，但这取决于表格中的其他内容。

仅显示列，GROUP BY 和 MAX() 之类的聚合函数可用于为每个“匹配”获取一个不同的行。

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

请注意，从 t2 返回 home 和 away 是多余的，因为 t1.home = t2.away 等。来自 t1 和 t2 的值是相同的，只是交换了 home 和 away .

要限制“反向”行，以便您得到 (bears,tigers) 而不是 (tigers,bears)，您可以指定一个额外的谓词，这样您只能得到反向的一个“边”：

AND t1.league_match_home_team < t2.league_match_home_team

---

跟进

（我的查询中有错字，第一个 JOIN 谓词应该在右侧指定 t2.。我相信 OP 发现了这个问题并修复了它。）

根据最新更新，为了消除结果集中的“镜像”反向行，您可以添加这样的谓词（如果您的查询有一个谓词，则在 GROUP BY 子句之后。）

  HAVING t1_id < t2_id

（与WHERE 子句不同，HAVING 子句可以引用分配给返回列的别名。）

如果您的查询中没有GROUP BY，则使用 WHERE 子句可能会获得更好的性能：

WHERE t1.match_id < t2.match_id

如果您获得两行中的哪一行无关紧要，那么它是小于还是大于比较都无关紧要。您选择比较哪一个 t1 和 t2 列（“id”、“home”或“away”）并不重要，只需要比较 t1 和 t2 之间的列，保证不同（所以你只会得到一面镜子。）

Answer 2

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