Query Selectivity Computation

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Query Selectivity Computation

gaurangtalwadkar

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May 6, 2010 at 3:49 am

#234665

Hi friends,
I m executing different queries with different parameter values from my application.
How to compute selectivity of a query with particular parameter?

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kinzent SSChasing Mays Points: 621 More actions · Answer 1

gaurangtalwadkar (5/6/2010)
Hi friends,
I m executing different queries with different parameter values from my application.
How to compute selectivity of a query with particular parameter?

distinct_values_count / all_values_count

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Thorn Bird...

gaurangtalwadkar SSC-Addicted Points: 437 More actions · Answer 2

I want to know whether der is any in-built function in SQL Server which gives selectivity of the query when the query is executed.

Grant Fritchey SSC Guru Points: 398909 More actions · Answer 3

A query is not selective or not. The data it is accessing may or may not be selective. I don't understand where you're trying to go with this.

You can query statistics and indexes to determine the selectivity of the underlying data. Is that what you're looking for?

"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt

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SQL Server Query Performance Tuning

gaurangtalwadkar SSC-Addicted Points: 437 More actions · Answer 4

Hi everybody,

how can I get query selectivity estimation in Sql server?

I m executing query from C# application where I have provide text editor to write sql queries.

Grant Fritchey SSC Guru Points: 398909 More actions · Answer 5

I still don't understand what you're asking for? A query has no selectivity. There is not a measured set of uniquely identifying data about a query. The data stored in tables and indexes have selectivity. You're going to have to better define what it is that you're looking for in order to get a specific answer.

"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt

Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning

Lowell SSC Guru Points: 323518 More actions · Answer 6

he had a similar thread on this;

i think the original poster is trying to get a formula like (#records matching my WHERE clause) / Total Records, but he thinks it is stored in the statistics of the server?

That's not the same as the statistics kept in SQL Server, and would vary for every query with a different WHERE statmenet.

Lowell

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