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Which index will SQL Server use to count all rows
This is a question that came up yesterday on Twitter: will SQL Server always do a table scan to find the result of SELECT COUNT (*) FROM mytable? The answer is no. The query processor will use the...
View ArticleTwo great blog series on joins and query plan operators
I was doing some research this morning for some query tuning on a client system and I came across a couple of blog series with some excellent posts for those looking to learn more about query plans...
View ArticleDBCC CHECKDB performance and computed-column indexes
[Edit 2016: The team ‘fixed’ the problem in SQL Server 2016 by skipping consistency checking these indexes unless WITH EXTENDED_LOGICAL_CHECKS is used.] It’s no secret that DBCC CHECKDB has some...
View ArticleReconciling set-based operations with row-by-row iterative processing
Yesterday in class we had a discussion around the conceptual problem of reconciling the fact that SQL Server does set-based operations, but that it does them in query plans that pass single rows around...
View ArticleSQLskills SQL101: Query plans based on what’s in memory
As Kimberly blogged about recently, SQLskills is embarking on a new initiative to blog about basic topics, which we’re calling SQL101. We’ll all be blogging about things that we often see done...
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