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Halloween Protection – The Complete Series I have written a four-part series on the Halloween Problem . Some of you wi...

The Halloween Problem – Part 4 The Halloween Problem can have a number of important effects on execution plans. In this...

The Halloween Problem – Part 3 The MERGE statement (introduced in SQL Server 2008) allows us to perform a mixture of ...

The Halloween Problem – Part 2 In the first part of this series , we saw how the Halloween Problem applies to UPDATE q...

The Halloween Problem – Part 1 Much has been written over the years about understanding and optimizing SELECT queries,...

Incorrect Results with Indexed Views If you use MERGE , indexed views and foreign keys, your queries might return incor...

A creative use of IGNORE_DUP_KEY Let’s say you have a big table with a clustered primary key, and an application that i...

Optimizing T-SQL queries that change data Most tuning efforts for data-changing operations concentrate on the SELECT s...

MERGE Bug with Filtered Indexes A MERGE statement can fail, and incorrectly report a unique key violation when: The ...

Cardinality Estimation Bug with Lookups Estimated row counts on Key or RID Lookups where a filtering predicate is app...

Why Doesn’t Partition Elimination Work? Given a partitioned table and a simple SELECT query that compares the partitio...

Compute Scalars, Expressions and Execution Plan Performance The humble Compute Scalar is one of the least well-underst...

Deletes that Split Pages and Forwarded Ghosts Can DELETE operations cause pages to split? Yes. It sounds counter-int...

Temporary Table Caching Explained SQL Server (since 2005) caches temporary tables and table variables referenced in ...

Temporary Table Caching in Stored Procedures Introduction Ask anyone what the primary advantage of temporary tables ...

Parallel Execution Plans Suck Summary : A deep dive into SQL Server parallelism, and a potential performance problem wi...

Query Optimizer Deep Dive - Part 4 This is the final part in a series of posts based on the content of the Query Optim...

Query Optimizer Deep Dive – Part 3 This is the third in a series of posts based on the content of the Query Optimizer ...

Query Optimizer Deep Dive – Part 2 This is the second in a series of posts based on the content of the Query Optimizer...

Query Optimizer Deep Dive - Part 1 This is the first in a series of posts based on the content of the Query Optimizer ...

Fun with Scalar and Vector Aggregates There are interesting things to be learned from even the simplest queries. For e...

Dynamic Seeks and Hidden Implicit Conversions A LIKE predicate with only a trailing wildcard can usually use an index...

Forcing a Parallel Query Execution Plan This article is for SQL Server developers who have experienced the special kind...

SQL Server Optimizer Bug with JOIN and GROUP BY I came across a SQL Server optimizer bug recently that made me wonder h...

Is Distinct Aggregation Still Considered Harmful? Back in 2008, Marc Friedman of the SQL Server Query Processor Team wr...