Things to consider when using SQL 2005 Query Notifications

When looking into why I was getting immediate notifications of a SQLDependancy being changed, I discovered a really nice MSDN2 page that documents the things to watch out for, Special Considerations When Using Query Notifications

Major things to note:

• If you use a query that doesn't comply, you'll get notified it is out-of-date immediately, so make sure you save the query results somewhere other than Cache[] when you do have to go to SQL Server.
• You must use two-part table names like dbo.Address, but you should be doing that anyway or you don't get pre-parsed queries. This means that you are obviously? only allowed to talk to one database.
• Don't use any SQL that requires aggregations or row-counting. This means aggregates like AVG, MIN, MAX, DISTINCT, COUNT(*). You can use SUM on non-nullable columns in the presence of a GROUP BY, but no ROLLUP or CUBE.

For full details, consult the article.