DISTINCT and UNION: What happens when you use them together?

When I was perusing my LinkedIn feed the other day, I came across this thread about using SELECT *. In one of the replies, Aaron Cutshall noted that: “Another real performance killer is SELECT DISTINCT especially when combined with UNION. I have a whole list of commonly used hidden performance killers!”

Multiple Defaults

Adding Defaults

What is Between?

How Many Can Be the Greatest

Generating a Series I

The Trigger Updated Column(s)

Techniques to query Azure SQL’s new JSON Datatype

The new JSON field type and new functions in Azure SQL brings a new world of possibilities for JSON manipulation in SQL Databases. These features are slated to be a part of SQL Server 2025 as well. Let’s analyze some practical uses of these features

Adding Lots of Dates

Purging Data from a Large Table in SQL Server

Purging data from a table is a common database maintenance task to prevent it from growing too large or to stay in compliance with data retention. When dealing with small amounts of data, this can be accomplished by a simple delete with no issues; however, with larger tables, this task can be problematic. Deleting records requires a lock that can block other processes from writing or even reading the data (depending on your isolation level). In this article I will share a technique I have used to work with some very large tables.