Some database operations can be performed in distinctly different manners, with different impacts on query performance. One important example of such an operation is calculating an aggregate. In this article, we’ll take a look at how aggregates can be “blocking” or “non-blocking”, how it affects memory allocation, and ultimately, what impact this has on your query.
The other day, I ran across the following issue: I was looking to split a value using upper case and lower case characters. Here’s an example query:
SELECT PATINDEX('%[a-z][A-Z]%', 'testValue' COLLATE Finnish_Swedish_CS_AS) AS offset
I expected this query to return the value 4, because at that offset in the string, there is a lower case character (t) followed directly by an upper case character (V). However, in practice, this query returns the value 1.
Understanding indexes in SQL Server can help you build much more efficient database solutions. Often, performance problems can be adressed with indexes, so knowing how indexes work and how to set them up for the best performance are a great asset in your optimization work.