如何根據多個欄位刪除SQL表中的重複項

Question

我有一張遊戲桌，描述如下：

+---------------+-------------+------+-----+---------+----------------+
| Field         | Type        | Null | Key | Default | Extra          |
+---------------+-------------+------+-----+---------+----------------+
| id            | int(11)     | NO   | PRI | NULL    | auto_increment |
| date          | date        | NO   |     | NULL    |                |
| time          | time        | NO   |     | NULL    |                |
| hometeam_id   | int(11)     | NO   | MUL | NULL    |                |
| awayteam_id   | int(11)     | NO   | MUL | NULL    |                |
| locationcity  | varchar(30) | NO   |     | NULL    |                |
| locationstate | varchar(20) | NO   |     | NULL    |                |
+---------------+-------------+------+-----+---------+----------------+

但是每場比賽在表中的某處都有重複的條目，因為每場比賽都在兩支球隊的賽程表中。是否有一個 SQL 語句可以用來根據相同的日期、時間、hometeam_id、awayteam_id、locationcity 和 locationstate 欄位查看並刪除所有重複？

Answer 1

您可以嘗試這樣的查詢：

DELETE FROM table_name AS t1
WHERE EXISTS (
 SELECT 1 FROM table_name AS t2 
 WHERE t2.date = t1.date 
 AND t2.time = t1.time 
 AND t2.hometeam_id = t1.hometeam_id 
 AND t2.awayteam_id = t1.awayteam_id 
 AND t2.locationcity = t1.locationcity 
 AND t2.id > t1.id )

這將在資料庫中僅保留每個具有最小 ID 的遊戲實例的一個範例。

Answer 2

您應該能夠執行相關子查詢來刪除資料。尋找所有重複的行並刪除除 id 最小的行之外的所有行。對於 MYSQL，需要使用內部連接（相當於 EXISTS 的功能），如下所示：

delete games from games inner join 
    (select  min(id) minid, date, time,
             hometeam_id, awayteam_id, locationcity, locationstate
     from games 
     group by date, time, hometeam_id, 
              awayteam_id, locationcity, locationstate
     having count(1) > 1) as duplicates
   on (duplicates.date = games.date
   and duplicates.time = games.time
   and duplicates.hometeam_id = games.hometeam_id
   and duplicates.awayteam_id = games.awayteam_id
   and duplicates.locationcity = games.locationcity
   and duplicates.locationstate = games.locationstate
   and duplicates.minid <> games.id)

要進行測試，請將從遊戲中刪除遊戲替換為從遊戲中選擇*。不要只是在資料庫上執行刪除:-)