删除重复的电子邮件记录

Question

我们需要编写一个 SQL 查询来删除名为 的表中的所有重复电子邮件条目Person，仅根据其最小 ID 保留唯一的电子邮件。

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+

Id是该表的主键列。

例如，运行查询后，上Person表应具有以下行：

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+

注意：执行SQL后输出的是整个Person表。需要使用delete语句。

这是我的答案：

delete Person
from Person p
left join 
    (select Id, Email 
     from
         (select 
              Id, Email,
              ROW_NUMBER() OVER(PARTITION BY Email ORDER BY Id) AS row_num
          from Person) as temp
     where row_num = 1) as temptwo on p.Id = temptwo.Id
where 
    temptwo.Id is null

但在我运行查询后，它不断告诉我此行存在语法错误：

ROW_NUMBER() OVER(PARTITION BY Email ORDER BY Id) AS row_num

有人能告诉我出了什么问题吗？

Answer 1

你可以只使用：

with todelete as (
      select p.*,
             ROW_NUMBER() OVER (PARTITION BY Email ORDER BY Id) AS seqnum
      from Person p
     ) 
delete from todelete
    where seqnum > 1;

也就是说，SQL Server 支持可更新的 CTE（以及子查询和视图），因此您不需要计算并连接回表。

编辑：

在 MySQL 中，您将使用：

delete p
    from p join
         (select email, min(id) as min_id
          from person pp
          group by email
         ) pp
         on p.email = pp.email and p.id > p.min_id;