Question

这是我的sql查询，用于删除重复行，但限制为

的行除外

DELETE n1 FROM v_news n1, v_news n2 WHERE n1.`id` > n2.`id` AND n1.`url` = n2.`url` ORDER BY n2.`id` LIMIT 100

但我得到的错误是这样的：

MySQL said: Documentation

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ORDER BY n2.`id` LIMIT 100' at line 1

我哪里错了？

提前致谢。

Answer 1

对于删除查询，无需包含order by和limit。所以只需删除这两个，然后尝试如下，

DELETE n1 FROM v_news n1, v_news n2 WHERE n1.`id` > n2.`id` AND n1.`url` = n2.`url`

Answer 2

正如documentation所解释的那样：

您可以在DELETE语句中指定多个表来删除行来自一个或多个表格，具体取决于WHERE中的条件条款。您无法在多表ORDER BY中使用LIMIT或DELETE。

换句话说，你的DELETE引用了两个表（好吧，同一个表两次），所以它被认为是多表删除。 ORDER BY是不允许的。

注意：您应该使用LIMIT而不是逗号来指定表格。

Answer 3

这种方法可行：

--use a temp table record the ids of the records you wish to delete
create temporary table if not exists newsIdsToDelete 
(
    Id bigint
    , PRIMARY KEY (id)
) ENGINE=MEMORY;

--populate that table with the IDs from your original query
select n1.`Id` 
into newsIdsToDelete
from v_news n1
inner join v_news n2 
on n2.`id` < n1.`id` 
and n2.`url` = n1.`url` 
order by n2.`id` 
limit 100;

--delete those records where the id's in the list of ids to be deleted
delete v_news 
where `Id` in (
    select `Id` 
    from newsIdsToDelete
);

--clean up the temporary table
drop temporary table if exists newsIdsToDelete;

（我没有MySql，而且我对该数据库的了解非常严格，所以请在使用前在安全的地方进行测试。）

sql：删除dupliacte行，除了有限制的行

3 个答案: