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Delete Duplicate Emails

Delete Duplicate Emails

作者: myang199088 | 来源:发表于2015-04-15 09:01 被阅读5次
    • Problem
      Write a SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id.
      +----+------------------+
      | Id | Email |
      +----+------------------+
      | 1 | john@example.com |
      | 2 | bob@example.com |
      | 3 | john@example.com |
      +----+------------------+
      Id is the primary key column for this table.
      For example, after running your query, the above Person table should have the following rows:
      +----+------------------+
      | Id | Email |
      +----+------------------+
      | 1 | john@example.com |
      | 2 | bob@example.com |
      +----+------------------+

    • Code
      delete from Person where Id not in (select * from (select min(Id) from Person group by Email) t);

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