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This article was originally published on 𝕏. I was asked recently why Halloween Protection was needed for data modification statements tha...

This article was originally published on 𝕏. SQL Server provides a way to select any one row from a group of rows, provided you write the...

This article was originally published on 𝕏. Introduction Microsoft encourages us not to use the datetime data type: Avoid using date...

Parallel Index Building Execution Plan SQL Server doesn't support parallel modifications to a b-tree index. That might sound surprising....

Empty Parallel Zones An empty parallel zone is an area of the plan bounded by exchanges (or the leaf level) containing...

SQL Server 2019 Aggregate Splitting The SQL Server 2019 query optimizer has a new trick available to improve the perfor...

A bug with Halloween Protection and the OUTPUT Clause Background The OUTPUT clause can be used to return results fro...

Pulling Group By Above a Join One of the transformations available to the SQL Server query optimizer is pulling a logic...

Apply versus Nested Loops Join SQL is a declarative language. We use SQL to write a logical query specification that d...

Cardinality Estimation for Disjunctive Predicates in SQL Server 2014 Introduction Back in January 2014, I wrote an art...

Incorrect Results Caused By Adding an Index Say you have the following two tables, one partitioned and one not: CREATE...

Two Partitioning Peculiarities Table partitioning in SQL Server is essentially a way of making multiple physical tables...

Aggregates and Partitioning The changes in the internal representation of partitioned tables between SQL Server 2005 an...

Working Around Missed Optimizations In my last post , we saw how a query featuring a scalar aggregate could be transfor...

Optimization Phases and Missed Opportunities There are two complementary skills that are very useful in query tuning. O...

Hello Operator, My Switch Is Bored This post is in two parts. The first part looks at the Switch execution plan operato...

Optimizer Limitations with Filtered Indexes One of the filtered index use cases mentioned in the product documentation ...

The Problem with Window Functions and Views Introduction Since their introduction in SQL Server 2005, window functions...

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

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