I've been using the Query Analyzer that comes with Microsoft SQL Server 2000 since it was first released and just discovered this trick today.
TIP: Query Analyzer - Selective Query ResultsIf you ever wish to run just a subset or portion of a query, highlight the portion of your query you want results for and click the "Execute Query" button (or hitting [F5].) Query Analyzer will then run just the portion of SQL code that's selected and display the results in the Results Grid.
This works great if you want to see what a query is doing without the where clause, or perhaps to see the results of an inner select statement. In the past I was always copying these to a new window to run. No more!
I can't believe I've never noticed this before. This is why occasionally I've gotten weird SQL errors that have been fixed by clicking somewhere in the SQL query window.