Question

我想删除表game中的重复项。有些条目具有相同的playerId和timeParameter，而gameId最低的条目应保留。

我可以用以下内容查询条目：

select a.`gameId` from `game` a
where not exists
  (select min(b.`gameId`) as m from `game` b
    group by b.`playerId`, b.`timeParameter`
    having m = a.`gameId`);

但是我不能在delete语句中使用alis a ：

delete from `game` a
where not exists
  (select min(b.`gameId`) as m from `game` b
    group by b.`playerId`, b.`timeParameter`
    having m = a.`gameId`);

获取语法错误：

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual
that corresponds to your MariaDB server version for the right syntax to use near 'a
where not exists
  (select min(b.`gameId`) as m from `game` b
    group by b.`' at line 1

此错误告诉我什么，但我知道我不能在删除语句中使用别名。

有解决方法吗？

Answer 1

您可以创建子查询并创建一个派生表

delete from game where gameId IN
(
select gameId from(
select a.`gameId` from `game` a
where not exists
  (select min(b.`gameId`) as m from `game` b
    group by b.`playerId`, b.`timeParameter`
    having m = a.`gameId`)
)tmp
)

Answer 2

如果您使用的是别名，那么这是正确的，并且每个MySQL文档都必须在DELETE语句中引用它。因此，请删除别名a或将DELETE语句设为

delete a from `game` a ...

引自Documentation

注意

如果声明表的别名，则必须在何时使用别名   参考表格：

DELETE t1 FROM test AS t1, test2 WHERE ...

Answer 3

使用@krishn patel idea创建一个临时表，这应该可行。

首先创建一个表 dontDeleteMe ，其中包含应保留的所有gameIds。

create table `dontDeleteMe` as
      select min(`gameId`) as `theId` from `game`
      group by `playerId`, `timeParameter`;

我可以将此表用于子查询：

delete from `game`
where `gameId` not in
  (select `theId` from `dontDeleteMe`);

之后我可以删除临时表：

drop table `dontDeleteMe`;

删除没有别名

3 个答案: