Deleting Duplicate batches of rows

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Deleting Duplicate batches of rows

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George Damien Varkey

Posted Monday, July 21, 2008 10:52 PM

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Comments posted to this topic are about the item Deleting Duplicate batches of rows

Post #538145

totlani.ritesh

Posted Monday, July 21, 2008 11:23 PM

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This code does not give proper results. I tried to work on this but its really untested bad work by the developer.

Post #538154

George Damien Varkey

Posted Thursday, August 21, 2008 5:31 AM

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Ritesh what is it that is not working, can you let me know.

Post #556417

Nick Hobbs

Posted Friday, October 03, 2008 1:19 AM

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I think this is a much more efficient example for deleting duplicate rows using a single query and not having to resort to using Cursors:

http://dipakjpatel.blogspot.com/2007/08/delete-duplicate-rows-using-single.html

Regards

Nick

Post #580094

tzara

Posted Friday, October 03, 2008 11:45 AM

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don't need a temp table. don't need cursors.

you can remove dups in one statement.

cheers.

Post #580485

fhanlon

Posted Friday, October 03, 2008 12:17 PM

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The code worked fine for me. There is more than one way to do this. So if you don't like this way try another but in terms of results this code works.

Francis

Post #580512

Nick Hobbs

Posted Monday, October 06, 2008 1:42 AM

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I am sure the code works fine, however the article implied that this is one situation where you have to use cursors - which are very inefficient if you can do it alternatively in a single query:

>>This code works in SQL Server 2005 and above, because it uses the delete top (N) statement. Although using a cursor is not always a good idea but there are situations where we have to use it.

I am sure the cursor method with copying the data to a temporary table is satisfactory for small sets of data. I was surprised however to see it listed as a featured article in SQL Server Central's daily newsletter. When having to regularly run a query against e.g. 1m+ records that may involve several tables, it helps to know if there are more efficient methods. I thought it was worth pointing to a more efficient method that I came across recently as this is not a situation where we have to use cursors.

Regards

Nick

Post #580932

irina-813672

Posted Tuesday, October 07, 2008 2:23 PM

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A much simpler way to remove duplicates would be to use SELECT DISTINCT * from tableName

Post #582176

Nick Hobbs

Posted Wednesday, October 08, 2008 1:23 AM

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SELECT DISTINCT * from tableName

While this gives you a list of records without the duplicates, it does not help much in deleting the duplicates. Additional code is still need to do something to remove the duplicates from the original table which this article addresses along with the other suggestions.

Post #582369

blairxy

Posted Friday, January 02, 2009 11:31 AM

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Thank you for sharing this. It was my introduction to cursors, and I was able to adapt it to keep my input table intact (by adding top(1) to another table, instead of deleting top @cnt).

Going forward, it does appear the common table expression approach linked by Nick has more promise.

All I wanted was something like 'Ignore row errors on insert'!

Post #629002

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