Solved

Delete double rows in mysql database

Posted on 2014-01-28
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Last Modified: 2014-01-28
Hi,

I have a table (table1) with 3 columns, id, text, flag.
The table contains tens of thousands of rows with some text.

Some of these rows are doubles.
I tried this query below to delete these double entries, but it runs for hours and deletes nothing.

DELETE n1 FROM table1 n1, table1 n2 WHERE n1.id > n2.id AND n1.text = n2.text

Does anybody have a better (working) and faster query?

Thanks!
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Question by:peps03
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4 Comments
 
LVL 35

Accepted Solution

by:
Dan Craciun earned 500 total points
ID: 39814407
Create an empty table2.

INSERT INTO table2 (id, text, flag) (SELECT id, text, flag FROM table1 GROUP BY table1.text)

HTH,
Dan
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Author Comment

by:peps03
ID: 39814421
Thanks Dan!
That worked! Very quickly!!

What was wrong with my query? A lot?
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LVL 35

Expert Comment

by:Dan Craciun
ID: 39814467
You query looked more like what a programmer would try than what SQL would expect.

You were JOINining your table with itself on the text field, which I guess was not indexed.

It created a huge table and I don't really know what MySQL was trying to do with it.
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Author Comment

by:peps03
ID: 39815088
Ok, thanks!
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