Cleveland DBA

SQL Server administration in Cleveland, OH

Stuff I learned … yesterday – statistics

Yesterday was a pretty full day between training and the ONSSUG June meeting immediately afterwards, so I didn’t get a chance to blog.  Anyway, I did learn something yesterday, but it didn’t come from the class I’m taking.  Erin Stellato (blog | twitter) gave a great presentation at ONSSUG about statistics.  I really wish she’d had more time because it was simply crammed with good information. 

Anyway, two key things I learned:

  1. Multicolumn statistics – Just what they sound like, statistics over multiple columns.  These are created by default when you create a composite index, but you can also create them yourself without an index using the CREATE STATISTICS command.  Helpful when you have queries that filter on multiple columns where no index exists.
  2. Filtered statistics – You can also put a filter on your statistics.  This is useful when you have a very large table but normally only query on a small subset of rows.  If these rows are highly selective, creating filtered statistics will help the optimizer choose the best path.

For more information on these 2 features or on statistics in general, check out Books Online.

June 8, 2011 Posted by | Features, SQL Tuning | , | Leave a comment