Slow distinct query in SQL Server over large dataset

Question

We\'re using SQL Server 2005 to track a fair amount of constantly incoming data (5-15 updates per second). We noticed after it has been in production for a couple months that on

Answer 1

An index helps you quickly find a row. But you're asking the database to list all unique types for the entire table. An index can't help with that.

You could run a nightly job which runs the query and stores it in a different table. If you require up-to-date data, you could store the last ID included in the nightly scan, and combine the results:

select type
from nightlyscan
union
select distinct type
from verybigtable
where rowid > lastscannedid

Another option is to normalize the big table into two tables:

talbe1: id, guid, typeid
type table: typeid, typename

This would be very beneficial if the number of types was relatively small.