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DELETE TOP syntax

Posted on 2003-10-22
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Last Modified: 2008-02-01
I was trying to do something like

DELETE TOP 3 FROM tblName

But the query anaylzer says invalid keyword by the word TOP.

I was going to use the SET ROWCOUNT method, such as

SET ROWCOUNT = 3
DELETE FROM tblName

But SQL Books Online suggested that you should replace any SET ROWCOUNT commands with the appropriate TOP version for any DELETE, INSERT, UPDATE.

So according to it, there is a DELETE TOP command, but I can't seem to find a reference anywhere on what the syntax is. Does anyone know if this is a valid command, and if so what the syntax is? By the way I'm using MS SQL 2000, thanks.
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Question by:Jeffbub213
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by:Jeffbub213
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Also, on a similar note, I tried using a dynamic query in the WHERE clause, but I guess this isn't allowed?

declare @numRows int                  --This would be an input parameter to a stored procedure actually
SET @sqlStr = 'SELECT TOP ' + CONVERT(varchar(2), @numRows) + ' field1 FROM tblName'
DELETE FROM tblName WHERE field1 IN (EXEC(@sqlStr))

But it complained about invalid syntax near the word EXEC, so I am guessing dynamic queries are not allowed in the WHERE clause of a SQL statement?


Also, I guess I forgot to mention above, but the number of rows to delete needs to be a variable. I used 3 as an example above, but this would actually be a passed in variable as I used in this example.
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Expert Comment

by:namasi_navaretnam
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DELETE FROM (SELECT TOP 3 FROM tblName)

Another example
DELETE authors
FROM (SELECT TOP 10 * FROM authors) AS t1
WHERE authors.au_id = t1.au_id

HTH

Namasi Navaretnam
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by:namasi_navaretnam
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DELETE Table1 t1
From (SELECT TOP 3 FROM Table1) as t2
WHERE t1.pk_id = t2.pk_id

HTH
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by:Anthony Perkins
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>>Also, I guess I forgot to mention above, but the number of rows to delete needs to be a variable.<<
Then use ROWCOUNT.  TOP requires it to be a constant.  You could use Dynamic SQL, but then you would be opening yourself up to lousy security and bad performance.

Anthony
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Author Comment

by:Jeffbub213
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Anthony-

Thats what I was planning on doing, but do you have any idea on why Books on Line suggests you not use the SET ROWCOUNT method??

Also just out of my own curiosity, there is no DELETE TOP 3 FROM tbl command right? I assume what the books on line meant was using TOP in the subquery, LIKE

DELETE FROM tbl WHERE fld IN (SELECT TOP 3 FROM tbl)

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Accepted Solution

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Anthony Perkins earned 250 total points
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>>but do you have any idea on why Books on Line suggests you not use the SET ROWCOUNT method??<<
The Select TOP clause was introduced with SQL 7 (as an aside, it had been in MS Access long before that), prior to that the only way to limit the rows was by using SET ROWCOUNT.  Obviously it is more efficient for queries to use TOP, providing that that value is constant, hence the recomendation.  But this still does not address the case when you are doing a Delete or when the value is variable.  For this you must use SET ROWCOUNT or resort to Dynamic SQL

>>there is no DELETE TOP 3 FROM tbl command right?<<
Take a look at the definition of DELETE in BOL you will see that there is no support for the TOP clause.

I hope this helps,
Anthony
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Assisted Solution

by:namasi_navaretnam
namasi_navaretnam earned 100 total points
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Try This,

SET @sqlStr = ' DELETE FROM tblName WHERE field1 IN ( SELECT TOP ' + CONVERT(varchar(2), @numRows) + ' field1 FROM tblName )'
EXEC(@sqlStr)

TOP is not supported with DELETE.

HTH,

Namasi Navaretnam
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Expert Comment

by:Anthony Perkins
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namasi_navaretnam,

Exactly, but then you are having to "resort to Dynamic SQL" and "opening yourself up to lousy security and bad performance" as I mentioned before.

Anthony
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Author Comment

by:Jeffbub213
Comment Utility
Thanks both Anthony and Namasi for your comments. I split the points between the two of you (and increased them a bit too). Since Anthony gave the answer I was looking for first, I gave him more of the points. But the method suggested by Namasi is a solution to the problem I posted. Thanks again.
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