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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. Background Since SQL Server indexed views don’t allow MIN or MAX aggregates, I recently fo...

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

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

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

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...

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

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

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...

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

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...

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