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Removing Duplicates in SQL Database Provided

I need to remove duplicates from a table that looks like this:

id           post_author    post_title
-----------------------------------------------------------------------------
21319        1              Youngstown State University
20535        1              Yo San University of Traditional Chinese Medicine
30268        29             Yo San University of Traditional Chinese Medicine
29747        29             Yeshiva University
21964        1              Yale University
29247        29             Yale University
29497        29             Xavier University of Louisiana
21916        1              Xavier University
29862        29             Xavier University
29860        29             Wright State University-Main Campus
20915        1              Wright State University-Lake Campus
21562        1              World Mission University
30267        29             World Mission University

Basically, if there are two records with the same post_title

, I need to delete one with post_author = 1

, but if post_title

unique, the record should be left as is.

How do I do this with a SQL query?

EDIT:

I tried the query suggested by Mureinik. The request looks like this:

DELETE t FROM wp_posts AS t 
WHERE t.post_author = 1 AND
EXISTS (SELECT * FROM wp_posts s 
                WHERE t.post_title = s.post_title
                AND s.post_authot != 1)

But I got the error:

[Err] 1093 - You can't specify target table 't' for update in FROM clause

What am I doing wrong?

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3 answers


You can set a condition on post_author = 1

where there is more than one post_title

with a temporary table:

CREATE TEMPORARY TABLE t_del AS SELECT post_title 
                     FROM t 
                     GROUP BY post_title 
                     HAVING count(post_title)>1;               

DELETE FROM t 
WHERE post_author = 1 
  AND post_title IN (select post_title FROM t_del) ;


SQL Fiddle here

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You can use the operator exists

:



DELETE FROM my_table t
WHERE  post_author = 1 AND
       EXISTS (SELECT *
               FROM   my_table s
               WHERE  t.post_title = s.post_title AND
                      s.post_author != 1)
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With operator in

:

delete from TableName where post_author = 1
and post_title in(select post_title from TableName group by post_title having count(*) > 1)
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