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Category: Syntax

Named Groups in T-SQL Regular Expressions

Published 2025-10-22 by Kevin Feasel

Andy Brownsword digs into a nice capability around using regular expressions:

Now that we’re on the cusp of adoption within SQL Server, it’ll be a valuable tool there too. However, after trying it out last week, one omission stood out – one of my favourite features for string parsing: Named Groups.

Where a usual expression can be used to match a string, Named Groups can also be used to extract details from the string. Using an example from Steve’s invitation where a PO number 20260720321433 begins with a year/month and then a number, this could be split with named groups:

Andy mentions the community displeasure for CLR and that displeasure annoys me to no end. I think 90% of the hysteria around CLR in SQL Server was a misunderstanding in terms and unwillingness to learn other programming languages. If you ever catch me in person, I’ll rant about it at length.

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HTML Parsing in T-SQL

Published 2025-10-22 by Kevin Feasel

Louis Davidson goes looking for list items:

From the title of “Favorite String Parsing”, I will say 100% it is using SQL Server 2025’s addition of Regular Expressions. Previously, parsing text in SQL Server was one of my least favorite things to do. Regular expressions will make it just a bit nicer, because it has a lot more power than SUBSTRING, LEFT, RIGHT, and CHARINDEX/PATINDEX. All generally “good enough” functions for a lot of the things you need to do, but often woefully inadequate for parsing large amounts of text.

Yeah, T-SQL RegEx is definitely a nicer approach, though HTML doesn’t have to follow the consistency rules of XML due to browsers being very forgiving in their interpretation of the language, so it’s easy to get tangled up trying to parse websites.

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String Comparisons in Oracle

Published 2025-10-16 by Kevin Feasel

Brendan Tierney gets comparing:

When comparing text strings we have a number of functions on Oracle Database to help us. These include SOUNDEX, PHONIC_ENCODE and FUZZY_MATCH. Let’s have a look at what each of these can do.

These are some classic word comparison techniques, but they work pretty well in specific circumstances.

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Concatenating String Values in SQL Server 2025

Published 2025-10-16 by Kevin Feasel

Louis Davidson plays around with the new string concatenation operator:

I was looking around for stuff to post about the other day, so I read through the latest What’s new in SQL Server 2025 and I found this:

|| (String concatenation) Concatenate expressions with expression || expression.

My interest was piqued to say the least. Using + to concatenate string data has always had its issues, and as much as I love the CONCAT function, it is kind of clunky to use versus a proper operator.

This is part of the ANSI SQL standard, and that standard does specify most of its behavioral patterns. Read on as Louis tries it out in a variety of circumstances.

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Tuning Window Functions in SQL Server

Published 2025-10-15 by Kevin Feasel

I have a new video:

In this video, I show you various techniques you can use to make window functions faster, including proper indexing and usage of batch mode. I also demonstrate the performance difference between RANGE and ROWS.

This wraps up my series on window functions, and although I pack a lot of content into the video, I highly recommend checking out the links for deeper dives into performance.

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Table Switching in SQL Server

Published 2025-10-14 by Kevin Feasel

Rebecca Lewis swaps in a bag of sand while snatching the golden idol:

Use ALTER TABLE … SWITCH to move very large tables instantly.  Yes.  I said instantly.  ALTER TABLE .. SWITCH doesn’t copy the data or physically move it.  It just reassigns the page ownership.  This means that only the metadata with the data pointer changes, and that’s why it completes in milliseconds and barely touches the transaction log.

There are some strict conditions around when you can use this technique, but it’s as powerful as Rebecca mentions.

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The Intricacies of COUNT()

Published 2025-10-09 by Kevin Feasel

Louis Davidson can easily get to 20:

I was reading LinkedIn posts the other day when I saw this blog about what was apparently an interview question about some forms of a COUNT aggregate function

This was apparently asked in an interview. What will each of these constructs do in a SQL statement:

COUNT(*) = ?
COUNT(1) = ?
COUNT(-1) = ?
COUNT(column) = ?
COUNT(NULL) = ?
COUNT() = ?

There’s one tricky bit in this set. Louis then takes it a bit further with CASE expressions and variables, so check out the post for the answers as well as those additional examples in T-SQL.

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Building an UPDATE … LIMIT in PostgreSQL

Published 2025-10-03 by Kevin Feasel

Laurenz Albe doesn’t have MySQL envy:

If you are reading this hoping that PostgreSQL finally got UPDATE ... LIMIT like MySQL, I have to disappoint you. The LIMIT clause is not yet supported for DML statements in PostgreSQL. If you want to UPDATE only a limited number of rows, you have to use workarounds. This article will describe how to do this and how to avoid the pitfalls and race condition you may encounter. Note that most of the following also applies to DELETE ... LIMIT!

Click through for what you can do in PostgreSQL instead. In T-SQL, we can use UPDATE TOP(n).

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