使用MySQL查找最新的重复ID

Question

我习惯做

SELECT email, COUNT(email) AS occurences
FROM wineries
GROUP BY email
HAVING (COUNT(email) > 1);

根据他们的电子邮件查找重复项.

但现在我需要他们的ID才能定义哪一个要删除.

第二个约束是:我只想要LAST INSERTED重复项.

因此,如果将2个条目与test@test.com作为电子邮件,并且它们的ID分别为40和12782,则它将仅删除12782条目并保留40条.

有关如何做到这一点的任何想法？我一直在捣碎SQL大约一个小时,似乎无法确切地找到如何做到这一点.

感谢,并有一个愉快的一天!

Answer 1

好吧,你有点回答你的问题.你似乎想要max(id):

SELECT email, COUNT(email) AS occurences, max(id)
FROM wineries
GROUP BY email
HAVING (COUNT(email) > 1);

您可以使用该语句删除其他人.删除时join有一个棘手的语法,你必须先列出表名,然后from用连接指定子句:

delete wineries
            from wineries join
            (select email, max(id) as maxid
             from wineries
             group by email
             having count(*) > 1
            ) we
            on we.email = wineries.email and
               wineries.id < we.maxid;

或者将其写为一个exists条款:

delete from wineries
    where exists (select 1
                  from (select email, max(id) as maxid
                        from wineries
                        group by email
                       ) we
                  where we.email = wineries.email and wineries.id < we.maxid
                 )