Selecting data in clustered index order without ORDER BY
- by kcrumley
I know there is no guarantee without an ORDER BY clause, but are there any techniques to tune SQL Server tables so they're more likely to return rows in clustered index order, without having to specify ORDER BY every single time I want to run a super-quick ad hoc query? For example, would rebuilding my clustered index or updating statistics help?
I'm aware that I can't count on a query like:
select *
from AuditLog
where UserId = 992
to return records in the order of the clustered index, so I would never build code into an application based on this assumption. But for simple ad hoc queries, on almost all of my tables, the data consistently comes out in clustered index order, and I've gotten used to being able to expect the most recent results to be at the bottom. Out of all the many tables we use, I've only noticed two ever giving me results in an unpredicted order. This is really just an annoyance, but it would be nice to be able to minimize it.
In case this is relevant because of page boundary issues or something like that, I should mention that one of the tables that has inconsistent ordering, the AuditLog table, is the longest table we have that has a clustered index on an identity column. Also, this database has recently been moved from SQL 2005 to SQL 2008, and we've seen no noticeable change in this behavior.
