December 2011 - Posts

• Forcing a Parallel Query Execution Plan

  This post is for SQL Server developers who have experienced the special kind of frustration, which only comes from spending hours trying to convince the query optimizer to generate a parallel execution plan.  This situation often occurs when making Read More... Posted Friday, December 23, 2011 10:09 AM by Paul White | 37 Comments

• SQL Server Optimizer Bug with JOIN and GROUP BY

  I came across a SQL Server bug recently that made me wonder how on earth I never noticed it before.  As the title of this post suggests, the bug occurs in common JOIN and GROUP BY queries, and while it does not cause incorrect results to be returned, Read More... Posted Tuesday, December 06, 2011 12:17 PM by Paul White | 7 Comments

• Is Distinct Aggregation Still Considered Harmful?

  Back in 2008, Marc Friedman of the SQL Server Query Processor Team wrote a blog entry entitled “Distinct Aggregation Considered Harmful” , in which he shows a way to work around the poor performance that often results simply from adding the keyword DISTINCT Read More... Posted Sunday, December 04, 2011 7:30 AM by Paul White | 10 Comments Filed under: Transformations, Query Plans, TSQL, Aggregates, Performance