Join on nvarchar column using LIKE

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Join on nvarchar column using LIKE

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praveen_vejandla

Posted Tuesday, January 22, 2013 12:49 AM

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UPDATE LII
SET value_exists = 1
FROM LII od
JOIN VPL sl
ON (sl.it like '%' + od.value + '%'
AND od.opr = 9 )
WHERE od.tn = 'VPL'
AND od.cn = 'it'

Is there anyway to rewrite above query for improved performance? I am joining two nvarchar columns (it, value) using LIKE and it seems very slow.

Thanks.

Post #1409840

ChrisM@Work

Posted Tuesday, January 22, 2013 12:59 AM

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UPDATE od
	SET value_exists = 1 
FROM LII od 
INNER JOIN VPL sl 
	ON sl.it LIKE '%' + od.value + '%' 
WHERE od.tn = 'VPL' 
	AND od.cn = 'it'
	AND od.opr = 9

The LIKE operator used with a wildcard on the left hand side of the search expression makes the join non-SARGable (Google it), which results in a table scan of table VPL. Do you really need the leading %?

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden
Exploring Recursive CTEs by Example Dwain Camps

Post #1409841

Bhuvnesh

Posted Tuesday, January 22, 2013 1:05 AM

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praveen_vejandla (1/22/2013)

send the index deifnition of Lil and VPL table

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Post #1409844

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