Date parsed: 18/10/2007 16:51:14
Date: Thu, 18 Oct 2007 16:51:14 -0000

We recently discovered a performance problem that was being caused by
the query optimizer using the auto created statistics on a column
instead of the statistics that we manually maintain. There is an index
on the column with the statistics set to norecompute and we manually
update the statistics because we want a 100% sample rate. With the
100% sample rate the index is very selective. However there is also
auto created statistics on the same column with a very small sample
rate and its selectivity is very low. For some reason the query
optimizer was looking at the auto created statistics.

According to books online, "when the AUTO_CREATE_STATISTICS database
option is set to ON (default), the Database Engine automatically
creates statistics for columns without indexes that are used in a
predicate." If that is correct then there should not be auto created
statistics on columns that have an index, right?