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Author: Kevin Feasel

Thoughts on Views

Published 2025-08-06 by Kevin Feasel

Joe Celko shares some thoughts on views, as well as recursive common table expressions:

VIEWs are an undervalued and underused feature in SQL. They basically consist of a query that has been given a name, and a parameter list, so can be used like an inline macro. Technically, you’re supposed to think of it as a virtual table. 

The idea of an inline macro or inline function goes way back to the first versions of Fortran and later BASIC. Depending on the product, the syntax might look like this: FN DOUBLE (N) = (N + N). You had to give the name of the Macro, a simple optional parameter list, assignment operator, usually an =, and the text of the computation. It was often important to put parentheses around the body of the macro, or to have a compiler that would do this for you. 

Read on for the article and a platform-agnostic coverage of views. My problem with views is that developers try to use them to cover a lot of ruin and then they ask why such a simple SELECT * FROM Something query is so slow.

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Reasons Regression Models Under-Perform

Published 2025-08-05 by Kevin Feasel

Ivan Palomares Carrascosa has a list:

In regression models, failure occurs when the model produces inaccurate predictions — that is, when error metrics like MAE or RMSE are high — or when the model, once deployed, fails to generalize well to new data that differs from the examples it was trained or tested on. While model failure typically shows up in one or both of these forms, the root causes can be more diverse and subtle.

This article explores some common reasons why regression models may underperform and outlines how to detect these issues. It is also accompanied by practical code excerpts using XGBoost — a robust and highly tunable ensemble-based regression model. Despite its popularity and power, XGBoost can also fail if not trained or evaluated properly!

These are high-level reasons but they’re good to keep in mind.

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Updates to Extensions in C# 14

Published 2025-08-05 by Kevin Feasel

The word miners in the NDepend blogging mines clue us in on an update to the C# language:

A few remarks:

  • If the extension is generic, the type parameter (if any) is specified immediately after the extension keyword.
  • The receiver ReadOnlySpan<T> span applies to one or more extension methods (or members) declared within the same extension block. This logical grouping is a core advantage of the new syntax, improving clarity and structure when extending a type.
  • As far as the C# compiler is concerned, the two methods Truncate() are strictly equivalent. Therefore, one must be commented out for the program to compile.
  • Notice the call to AsSpan() in the first line. Extension methods require the receiver type to match exactly ReadOnlySpan<T>, hence it doesn’t apply to string unless you explicitly cast. This is not specific to the new syntax but worth mentioning.

Read on for examples of how extension methods and extension members will open up opportunities to improve existing C# code.

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Regular Expression-Based String Splitting in SQL Server 2025

Published 2025-08-05 by Kevin Feasel

Aaron Bertrand splits a string:

SQL Server users have been asking for native regular expression support for over two decades. There are third-party Common Language Runtime (CLR) modules that offer this functionality, but these can be complicated to install and simply aren’t possible in some environments. I want to split a string using a regular expression instead of a static string. Will that be possible in SQL Server 2025, without CLR?

Must not rant about CLR. Must not rant about CLR. Must not rant about CLR. (By the way, if you ever catch me in person, get me going about how CLR got the short end of the stick and how the ‘modern’ forms of the Common Language Runtime in SQL Server are not great.)

Aaron tries out a function built into SQL Server that allows you to split strings into result sets using a regular expression to perform the splitting, and shows off some of the more complicated scenarios that this can solve over a normal STRING_SPLIT() function call.

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Using a Child Pipeline Variable in a Parent Pipeline in Fabric Data Factory

Published 2025-08-05 by Kevin Feasel

Justin Bird passes back some information:

I answered a question on the Fabric community on return variables recently and thought I would expand upon it in a blog post. The question was how to use a variable derived in a child pipeline downstream in the parent pipeline. The person was specifically deriving a json object and wanted to iterate on the values in the parent pipeline.

Click through for the solution.

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Performance Optimizing PostgreSQL for RTABench Q0

Published 2025-08-05 by Kevin Feasel

Andrei Lepikhov gets under the hood:

I wanted to explore whether Postgres could be improved by thoroughly utilising all available tools, and for this, I chose the RTABench benchmark. RTABench is a relatively recent benchmark that is described as being close to real-world scenarios and highly selective. One of its advantages is that the queries include expressions involving the JSONB type, which can be challenging to process. Additionally, the Postgres results on RTABench have not been awe-inspiring.

Ultimately, I decided to review all of the benchmark queries, and fortunately, there aren’t many, to identify possible optimisations. However, already on the zero query, there were enough nuances that it was worth taking it out into a separate discussion.

Click through for a dive into this particular query and what Andrei did and some of the lessons you can draw from it.

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No More TLS 1.1 in Microsoft Fabric

Published 2025-08-05 by Kevin Feasel

Nisha Sridhar makes an announcement:

We have officially ended the support for TLS 1.1 and earlier on the Fabric platform. As previously announced, starting July 31, 2025, all outbound connections from Fabric to customer data sources must use TLS 1.2 or later.

This update follows our earlier announcement in the TLS Deprecation for Fabric blog, where we outlined the rationale and timeline for this transition.

Read on to see what you might need to do to keep up to date.

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Learning RegEx with Louis Davidson

Published 2025-08-04 by Kevin Feasel

Louis Davidson has a few blog posts for us to catch up on. So far, this is a four-part series on regular expressions and SQL Server.

Part 1 covers simple pattern matching:

I have never once written an regular expression prior to a couple of articles on this blog. And truth be told, when I published those blogs, I got the expression wrong because it seemed to work, and it was what Copilot told me would work. If you are new like me and/or your code is important, test with lots of cases. I obviously fixed that code (thankfully the conclusions were right).

So no, I have never. LIKE does 99% of what I need in a simple manner, and .8% of the time in a complex way, so I never really thought about it too much. I suspect that will be the case even now in SQL, but like any good student, it is time to change my knowledge of regular expressions.

Part 2 covers repeating patterns:

In this blog, I want to look for strings that have 1 or more instances of a repeating pattern. For example, say you want to look for something like the following:

LIKE'%FredFredFred%'

--(or any fixed or unlimited length of a, and only a)
LIKE'%aaaaaaaaaaaaaaa%'or'%aaaaaaa%'

Part 3 looks at matching sets of characters:

In this article, we are going to take an initial look at what are referred to as “character classes” or “character sets” in Regular Expressions. They are commonly used when looking for data to be in a certain format. For example:

We are going to look at how to set a filter for 'lll-ll-lln' and/or 'lll-ll-lll' (where l is letter and n is numeric).

And part 4 deals with negation:

In Part 3, I covered some of the basics of using character classes/sets. (I do tend to say sets.) This allowed us to do things like find words that start with a, b, c, d or e. This is done using: ^[a-e] or ^[abcde]. Now I want to look at two new things (one of which looks really similar to the previous classes but does things very differently.:

  • Negated character classes – Look for strings that don’t have a particular character in them
  • Perl character classes – shorthand for certain types of characters

Regular expressions can be very challenging to learn and even more challenging to troubleshoot and ensure there are no missing corner cases. But they offer an enormous amount of power and that makes it all worthwhile.

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Working with Microsoft’s First-Party Python Driver

Published 2025-08-04 by Kevin Feasel

Sebastiao Pereira takes a look at mssql-python:

Python can connect to SQL Server using drivers like pyodbc and pymssql. However, Microsoft recently released a new Python driver called Python Driver for SQL Server or mssql-python. Currently in preview, Microsoft describes it as “the only first-party driver.” So, what’s this new driver all about, and how do you use it? Learn how to configure Python to connect to SQL Server with this new driver.

My standard caveat applies: this looks pretty neat, assuming that Microsoft actually continues to support it. Sebastiao mentions that it requires Python 3.13, but the docs say 3.10 or later. If the former is true, it might be a while before a lot of shops actually use it. But if the latter is true, most Python installations should support the driver out of the box.

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