Paul White goes deep on grouped aggregation pushdown, and explains examples where this optimization is unsuccessful or simply not attempted, using the undocumented command DBCC CSINDEX.
Itzik Ben-Gan asks you to invest in SQL Server's future by voting for Row Pattern Recognition, a potential T-SQL syntax extension he deems the next step in the evolution of window functions.
Paul White explains why the IGNORE_DUP_KEY index option on a clustered index can result in much poorer performance than for a nonclustered unique index.
Itzik Ben-Gan reviews the logic and performance of some novel submissions to a reader challenge involving joining between two tables based on closest match.
