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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...

Inside the Optimizer: Row Goals In Depth Background One of the core assumptions made by the SQL Server query optimizer...

Viewing Another Session’s Temporary Table Is it possible to view the contents of a local temporary table, created on...

The Impact of Non-Updating Updates From time to time, I encounter a system design that always issues an UPDATE against...

Iterators, Query Plans, and Why They Run Backwards Iterators SQL Server uses an extensible architecture for query opti...

An Interesting MERGE Bug Investigating an optimizer transformation that exposes a bug in SQL Server’s MERGE implementa...

Inside the Optimizer: Constructing a Plan – Part 4 More undocumented ways to explore how the query optimizer works.

Inside the Optimizer: Constructing a Plan – Part 3 Presenting an undocumented Dynamic Management View we can use to ide...

Inside the Optimizer: Constructing a Plan - Part 2 Continuing the series of posts looking at how the optimizer matches ...

Inside the Optimizer: Constructing a Plan - Part 1 For today’s entry, I thought we might take a look at how the optimiz...

Ranking Function Optimizer Transformations In my last post I showed how SQL Server 2005 and later can use a Segment ...