Question

Duplicate of How to delete duplicate records in mysql database?

   id  |  name   |      link
    1     bla     www.google.com
    2     lal     www.stackoverflow.com
    3     afs     www.google.com
    4     sds     www.microsoft.com

In my database there some rows with same link. I want to delete one of that rows with the same link.

Such as, in my example I want to delete the row with the id = 3 but I want to keep id = 1.

How can I do this?

by the way there are 5840 rows. and I don’t know which are the same. I need a code to compare them

Answer 1

trick is to keep latest value with comparing ids

DELETE FROM table_name t1, table_name t2 WHERE t1.name = t2.name and t1.link = t2.link and t1.id < t2.id

It’s just and idea, this is a fully functional example on my oracle environment (I haven’t use db few weeks, so I’m trying to minimalize the query right now, sorry)

SQL> select * from dup;

    ID    STH       STH2
---------- ---------- ----------
     1     45         45
     2     45         56
     3     45         45
     4     14         56
     5     14         56


DELETE FROM dup where id in (SELECT DISTINCT t1.id FROM dup t1, dup t2 WHERE t1.sth = t2.sth and t1.sth2 = t2.sth2 and t1.id < t2.id);

SQL> select * from dup;

    ID    STH       STH2
---------- ---------- ----------
     2     45         56
     3     45         45
     5     14         56