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Like operator - Query performance issue


Like operator - Query performance issue

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Krishna1
Krishna1
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Dear All

Have a table with 15 million rows. And Almost 15 columns. I am using following query. which is very slow. This table is having cluster index

select top 100
from TABLE
where COLUMN1 like '%xxx%'
OR Column2 like '%xxx%'
.
.
.
OR Column12 like '%xxx%'

Is there a better way to get the same result.
twin.devil
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The % at the start means your search needs to read every row and look for a match. If you really need that kind of search you should look into using a full text index.



There is also a bug related with LIKE Statement. you can look to that as well.

http://support.microsoft.com/kb/2847467

Hope it helps.
gstarsaini
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Partitions would be helpful.Then you could also restrict conditions in where clause
Krishna1
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create full text index fro all the 15 columns?
Krishna1
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sorry did not understand about partitionong
GilaMonster
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Partitioning is unlikely to help at all.

Unless you can add some SARGable predicates (predicates where SQL can use indexes to reduce the rows it has to read), there's probably not much that can be done. LIKE with a leading wildcard requires SQL to read every row, so that query will read every row of the table.

Full text may or may not help. Try it out and see.


Gail Shaw
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SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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Grant Fritchey
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Partitioning is not primarily a performance tuning mechanism. It is primarily a data management mechanism. There are cases where you can get performance improvements, but you need to remember that it's not designed to do that. It's designed to help with large scale data management.

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As an aside, it seems odd that you are searching so many of those columns. Can you show us what the data looks like?

“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
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gsaini 95591 (3/31/2014)
Partitions would be helpful.Then you could also restrict conditions in where clause


We're talking about a leading wildcard in 12 different columns. As the others have suggested, parititioning wouldn't help that at all.

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

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Krishna1 (3/31/2014)
create full text index fro all the 15 columns?

Sounds like a good option, have used this in similar situations before with good results.
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