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Finding the Statistics Used to Compile an Execution Plan In this post, I show you how to determine the statistics objec...

Can a SELECT query cause page splits? The SQL Server documentation has this to say about page splits : When a new row...

SQL Server, Seeks, and Binary Search The following table summarizes the results from my last two articles, Enforcing Un...

Avoiding Uniqueness for Performance In my last post, Enforcing Uniqueness for Performance , I showed how using a unique...

Enforcing Uniqueness for Performance A little while back, I posted a short series on seeks and scans: When is a Seek ...

Join Performance, Implicit Conversions, and Residuals Introduction You probably already know that it’...

Bitmap Magic (or… how SQL Server uses bitmap filters) Question Can a parallel query use less CPU than the same serial...

Undocumented Query Plans: The ANY Aggregate As usual, here’s a sample table: CREATE TABLE #Example ( pk numeri...

Undocumented Query Plans: Equality Comparisons The diagram below shows two data sets, with differences highlighted: T...

How Parallelism Works in SQL Server You might have noticed that January was a quiet blogging month for me. Part of the...

SQL Server Bug: Slow T-SQL Sums and Averages It’s a curious thing about SQL that the SUM or AVG of no items (an empt...

Advanced T-SQL Tuning: Why Internals Knowledge Matters There is much more to query tuning than reducing logical reads a...

I see no LOBs! Is it possible to see LOB (large object) logical reads from STATISTICS IO output on a table with no LO...

Seeking Without Indexes A seek can contain one or more seek predicates , each of which can either identify (at most) on...

So…is it a Seek or a Scan? You might be most familiar with the terms ‘Seek’ and ‘Scan’ from the graphical plans produce...

When is a Seek not a Seek? The following script creates a single-column clustered table containing the integers from 1 ...

Beware Sneaky Reads with Unique Indexes I saw a question asked recently on the #sqlhelp hash tag: Might SQL Server ...

Heaps of Trouble? Brad Schulz recently wrote about optimizing a query run against tables with no indexes at all . The...

Myth: SQL Server Caches a Serial Plan with every Parallel Plan Many people believe that whenever SQL Server creates an ...

The Case of the Missing Shared Locks This post covers a little-known locking optimization that provides a surprising an...

Sequence Tables It is frequently useful to generate sequences of values within SQL Server, perhaps for use as surrogat...

A Tale of Two Index Hints If you look up Table Hints in the official documentation, you’ll find the following stateme...

Inside the Optimizer: Plan Costing A detailed look at costing, and more undocumented optimizer fun. The SQL Server que...

Sorting, Row Goals, and the TOP 100 Problem When you write a query to return the first few rows from a potential result...

Row Goals and Grouping You might recall from Inside the Optimizer: Row Goals In Depth that query plans containing a r...