刪除sql中的重複項：您無法在FROM子句中指定目標表'表'進行更新

Question

我想從我的mysql表中刪除所有重複的記錄。我想這一點，但我有followint錯誤：

You can't specify target table 'maTable' for update in FROM clause.

我已經看到這另一個主題，但我希望你能看到我在做什麼毛病我的疑問，我怎樣才能使它工作

DELETE 
FROM maTable 
WHERE id_table IN (SELECT id_table 
      FROM maTable GROUP by id_table 
     HAVING COUNT(id_table)>1) 

Answer 1

嘗試包裹IN查詢在子查詢：

DELETE 
FROM maTable 
WHERE id_table IN (
    SELECT id_table 
    FROM (SELECT id_table 
     FROM maTable 
     GROUP by id_table 
     HAVING COUNT(id_table)>1) AS t) 

Demo here

Answer 2

這是MySQL的限制。它周圍的一種方法是使用join：

DELETE m 
    FROM maTable m JOIN 
     (SELECT id_table, COUNT(*) as cnt 
      FROM maTable 
      GROUP BY maTable 
     ) mm 
     ON mm.id_table = m.id_table 
    WHERE cnt > 1; 

如果要刪除所有，但重複的一個（即保持一個值），那麼最好是有某種獨特的列如創建日期：

DELETE m 
    FROM maTable m LEFT JOIN 
     (SELECT id_table, min(creation_date) as mincd 
      FROM maTable 
      GROUP BY maTable 
     ) mm 
     ON mm.id_table = m.id_table AND m.creation_date = mm.mincd 
    WHERE mm.id_table IS NULL;