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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 Update execution plans are not something the T-SQL statement writer has much co...

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....

Erik Darling ( @erikdarlingdata ) shared an interesting SQL Server execution plan with me recently. The demo script is at the end of this ar...

More Consistent Execution Plan Timings in SQL Server 2022 The updated showplan schema shipped with SSMS 19 preview 2 c...

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

Incorrect Results with Parallel Eager Spools and Batch Mode You might have noticed a warning at the top of the release ...

Closest Match with Sort Rewinds In When Do SQL Server Sorts Rewind? I described how most sorts can only rewind when th...

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...

Batch Mode Bitmap Demos This is a companion post to my main article Batch Mode Bitmaps in SQL Server . This post provid...

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

Parameter Sniffing, Embedding, and the RECOMPILE Options Parameter Sniffing Query parameterization promotes the reuse ...

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...

Improving Partitioned Table Join Performance The query optimizer does not always choose an optimal strategy when joinin...