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Editorial Team
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Asked: 2026-06-17T19:10:35+00:00

Lets imagine two tables: username id, name 1 username1 2 username1 3 username2 emails

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Lets imagine two tables:

username
 id, name
 1   username1
 2   username1
 3   username2

emails
 id, user, name
 1   1     assdf@sdf.hu
 2   2     afgdf@sdf.hu
 3   3     gfg@sdf.hu

the problem is there are duplicated entries. I cant simply drop them, because records are connected to them, so they get lost. (for example afgdf@sdf.hu email address). How to solve it?

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1 Answer

  1. Editorial Team

    SQLFiddle demo

    First you should update table emails to replace user with right values to eliminate values to be deleted.

    update emails set user=(select min(id) 
                        from username 
                       where name=
                      (select name from username where id=emails.user));

    Now delete from username table duplicate records. We keep only records with MINIMAL id for each name:

    DELETE t1.*
FROM username t1
LEFT JOIN (select min(id) mid from username group by name) t2 ON t1.ID = t2.mid
WHERE t2.mid is null;
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