PK And Index

I have a primary key that comprises 2 columns (lets say ReportDate and
Symbol).

I know that if I submit a statement like SELECT * FROM T1 WHERE
ReportDate = '20031219' AND Symbol = 'XYZ' it will use the index.

But how about the statement SELECT * FROM T1 WHERE Symbol = 'XYZ'?

Do I need to create another index on symbol alone?Jason (JayCallas@.hotmail.com) writes:
> I have a primary key that comprises 2 columns (lets say ReportDate and
> Symbol).
> I know that if I submit a statement like SELECT * FROM T1 WHERE
> ReportDate = '20031219' AND Symbol = 'XYZ' it will use the index.
> But how about the statement SELECT * FROM T1 WHERE Symbol = 'XYZ'?
> Do I need to create another index on symbol alone?

For best performance, yes.

But the query may use the existing index, if the index is non-clustered.
If SQL Server finds that XYZ is not a very common value, it may opt
scan the index to find the rows. This is faster than scanning the entire
table. If the value is common, however, the bookmark lookups will be
more expensive than scanning.

If the existing index is clustered, it can not help to speed up the
retrieval. Ah, that wasn't completely true, either. Because if the
there is a non-clustered index on the table as well, the keys of the
clustered index appears in the non-clustered index, so SQL Server can
scan that index.

--
Erland Sommarskog, SQL Server MVP, sommar@.algonet.se

Books Online for SQL Server SP3 at
http://www.microsoft.com/sql/techin.../2000/books.asp|||To add to Erlands response. You could check the Execution Plan when using
Query Analyzer to see how SQL Server is using your indexes.

BZ

"Jason" <JayCallas@.hotmail.com> wrote in message
news:f01a7c89.0312190912.1c1ea341@.posting.google.c om...
> I have a primary key that comprises 2 columns (lets say ReportDate and
> Symbol).
> I know that if I submit a statement like SELECT * FROM T1 WHERE
> ReportDate = '20031219' AND Symbol = 'XYZ' it will use the index.
> But how about the statement SELECT * FROM T1 WHERE Symbol = 'XYZ'?
> Do I need to create another index on symbol alone?