drbae3964 2010-12-15 18:34
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如何列出数据库中的重复条目

how can i write a query to list duplicate entries in a database from the same category. The duplicates have the same value in the "name" column. I need to list only the duplicates in the same category so I can then delete the duplicate.

I am using this example from a search

 SELECT email FROM tableName GROUP BY email HAVING count(email) > 1

That works for getting duplicates but it gets all duplicates, how can i rewrite it to get the duplicates from the same categories. In the above example, if i have an email that exists in the cat 1 and cat 4, it will be shown as duplicate, which is not the case. It should only list duplicates if the email exists twice or more in cat 1, or twice and more in cat 4 and so on.

Thanks.

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  • doucigua0449 2010-12-15 18:41
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    You can add more than one column to a group by. I.E.

    SELECT email, category from tableName GROUP BY email, category HAVING count(email) > 1
    

    That will show the email and category only where the email and category are both duplicate (I.E. same email twice with same category).

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