从子选择中删除id为comming的行（使用SQLite，使用MySQL失败）

我有两张桌子：桌上的“游戏”和桌上的“玩家”。玩家通过游戏id引用游戏。一个游戏可以包含多个玩家。我的应用程序应该与MySQL和SQLite一起工作，我不在这些表上使用外键

我的应用程序允许通过删除游戏表中的一行来删除游戏。所以，一些玩家可能有一个参考（游戏id）到一个不再存在的游戏，这对我来说很好

现在我想删除“孤儿”玩家：任何出现在玩家身上的无效游戏ID都必须被删除。如果可能的话，我想在一个查询中完成它

我找到了一个使用SQLite的有效解决方案：

delete 
from 
  player 
where 
  player_id in (
    select
    P.player_id
    from player P
    left join game G on G.game_id = P.game_id
    where G.game_id is null
  )

但MySQL中的同一查询返回一个错误：

#1093 - You can't specify target table 'player' for update in FROM clause

如果in子句包含同一表中的引用，则似乎无法删除表中的记录

如何在一个与MySQL和SQLite兼容的查询中实现这一点

---

更改您的

删除

查询，如下所示：

delete 
from 
  player 
where 
  player_id in (
    select * from ( 
        select
            P.player_id
            from player P
            left join game G on G.game_id = P.game_id
            where G.game_id is null
        ) as t
  )

原因是无法处理锁定删除的表。使用上述技巧，Mysql创建一个临时表，并允许处理Delete命令。

两个选项是可能的

使用额外的子查询

查询

delete 
from 
  player 
where 
  player_id in (
    select 
     player_alias.player_id
    from (
      select
      P.player_id
      from player P
      left join game G on G.game_id = P.game_id
      where G.game_id is null
    ) AS player_alias
  )

DELETE 
 player.*
FROM (
  select
   P.player_id
  from player P
  left join game G on G.game_id = P.game_id
  where G.game_id is null  
) AS player_delete
INNER JOIN 
 player 
ON
 player.player_id = player_delete.player_id

  delete
    P.*
  from
    player P
  left join game G on G.game_id = P.game_id
  where G.game_id is null 

看

或者使用联接执行“多个”表删除，我会选择这样做，因为使用正确的索引优化查询会更好

查询

delete 
from 
  player 
where 
  player_id in (
    select 
     player_alias.player_id
    from (
      select
      P.player_id
      from player P
      left join game G on G.game_id = P.game_id
      where G.game_id is null
    ) AS player_alias
  )

DELETE 
 player.*
FROM (
  select
   P.player_id
  from player P
  left join game G on G.game_id = P.game_id
  where G.game_id is null  
) AS player_delete
INNER JOIN 
 player 
ON
 player.player_id = player_delete.player_id

  delete
    P.*
  from
    player P
  left join game G on G.game_id = P.game_id
  where G.game_id is null 

看

两次删除都将保留

| player_id |       name | game_id |
|-----------|------------|---------|
|       111 |  PlayerOne |      G1 |
|       222 | Player Two |      G1 |

编辑

使用联接的“多”表删除可以重写（更）简单的offcource
作为额外的加号，这对性能和内存来说也是更好的。假设MySQL可以使用正确的索引来进行查询，因为

FROM（SELECT..）as）也会迫使MySQL将其作为

查询

delete 
from 
  player 
where 
  player_id in (
    select 
     player_alias.player_id
    from (
      select
      P.player_id
      from player P
      left join game G on G.game_id = P.game_id
      where G.game_id is null
    ) AS player_alias
  )

DELETE 
 player.*
FROM (
  select
   P.player_id
  from player P
  left join game G on G.game_id = P.game_id
  where G.game_id is null  
) AS player_delete
INNER JOIN 
 player 
ON
 player.player_id = player_delete.player_id

  delete
    P.*
  from
    player P
  left join game G on G.game_id = P.game_id
  where G.game_id is null 

请参见
谢谢您的帮助。最新的查询不适用于SQLite，因此我使用了select in select技巧。“最新的查询不适用于SQLite”哦，是的@JayMore I mist“我如何在一个查询中实现这一点，并与MySQL和SQLite兼容？”