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Category: T-SQL Tuesday

The Five Stages of Code Review Grief

Published 2023-07-13 by Kevin Feasel

Shane O’Neill has an experience:

You have code that keeps coming up as a high consumer of CPU on our systems? OK?

It had gotten to the stage where it kept appearing in sp_WhoIsActive? What’s that? And should it not be “whom is active”? Well, agree to disagree.

Let’s see the code so. Wow, that’s a small scroll bar! Yeah, that’s one of ours.

I should note that “Who is active?” is correct, as the sessions we are inquiring after are the subject of the question rather than the direct or indirect object, and there is no prepositional phrase which would affect the decision.

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Understanding String Concatenation with FOR XML PATH

Published 2023-07-12 by Kevin Feasel

Brent Ozar did some noodling:

The first time I saw FOR XML PATH being used to generate a comma-delimited list, I think I stared at it, shook my head to clear the cobwebs, stared at it some more, and then closed the code editor thinking it was complete witchcraft.

And that same thing probably happened the next several times, too.

But eventually, I took a deep breath and read the code more closely to understand what it was doing.

I do like to joke that this is cryptic code that gets handed down from generation to generation, with each generation saying “Don’t touch the code, for you do not understand it.” But as of SQL Server 2017, you don’t need to do this anymore and can use STRING_AGG().

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The Tally Table Splitter

Published 2023-07-12 by Kevin Feasel

Steve Jones talks tally tables:

That being said, years ago I got an article from Jeff Moden on the tally table. I hadn’t used this, and was fascinated. I know Itzik had written about numbers tables early on, but it hadn’t caught my attention. However, in a follow-up, Jeff wrote about a splitter function, which would use the tally table to split strings efficiently. This is the function (credit to Jeff in his article):

Click through for that function. The CLR-based tally table function is still faster, but if you can’t have CLR in your environment, and you split strings so frequently that you need a splitter, and STRING_SPLIT() just doesn’t do it for you (or you’re on an older version of SQL Server), this is a good solution. It’s also the foundation for a principle I have with T-SQL query tuning: sometimes you need to think in terms of pivoted or unpivoted data and operate on it versus the raw data. Here, we’re unpivoting a string into one row per character to get what we need out of it much more efficiently than if we tried to work the string by itself.

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T-SQL Query Transformations and Performance

Published 2023-07-12 by Kevin Feasel

Erik Darling isn’t satisfied with “good enough”:

Query tuning is hard work, especially when queries run for a long time and you have to test various changes trying to get it down to a reasonable runtime.

There are, of course, things you pick up intuitively over time, and figuring out where problems in actual execution plans has gotten easier with operator runtimes.

Beyond basic query tuning intuition comes the really creative stuff. The stuff you’re amazed anyone ever thought of.

Click through for two really interesting examples.

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A Story of Bad Data Modeling

Published 2023-07-12 by Kevin Feasel

Kendra Little unravels a puzzle:

I double-checked my queries. Had I goofed in my sql? Nope. Next, I looked into if some of the data was in an inconsistent state.

What I found was worse than what I’d imagined. As a data person, it made me feel sad and icky.

That’s because it’s usually not too hard to clean up bad data. It’s almost always much harder to fix a badly designed data model which is already established in production.

Read on for a tale as old as time: the clarion call of expediency now causing pain later.

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Getting Last-Used Report Parameters for SSRS

Published 2023-04-14 by Kevin Feasel

Brian Bønk shares some history:

A couple of years back I needed to find the latest used parameters from a reporting services – SSRS (yes, it is old!) report. The functionality was to find the latest used parameters for all parameters dynamically and use them as the default values for each parameter in the report, when tjhe user opened the report. If the uesr had not used the reprot before, it should ask for the parameters.

This was a alot of fun for me to do, as I needed to query the internal tables from the reporting services database. The tables ExecutionLogStorage and the Catalog was on play. This due to the fact that I needed the active user’s latest used parameter values from each specific report and this in runtime when the report was opened.

Click through to see how Brian did it.

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Building a Wordle Solver in Powershell and T-SQL

Published 2023-04-12 by Kevin Feasel

Shane O’Neill takes this T-SQL Tuesday to heart:

I got swept up in that wave for a while in the same way I got swept up in the other trends of my time, like Pokemon, Sodoku, and Angry Birds.

Eventually, I stopped when I found a PowerShell script by Kieran Walsh ( github | twitter ) where you could narrow down to the correct answer by putting in the results of your guess each round.

This hack led to me realising how much time I was spending on Wordle and that I should stop, much like I did with Pokemon, Sodoku, and Angry Birds.

So, what better thing to do than to try and recreate that PowerShell script in T-SQL

And given Shane’s time restriction, I’d say the end result is a good one.

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Stuffing Characters with STUFF

Published 2023-04-12 by Kevin Feasel

John McCormack tries out some stuff:

I don’t often go down code based rabbit holes, its just not what I do day to day but a while back, someone asked on twitter’s #sqlhelp hashtag if there was a character length limit to the STUFF function. The documentation didn’t have an answer. For that reason only, I decided to take a look. 

Click through to see what John learned along the way.

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T-SQL and Fun Puzzles

Published 2023-04-11 by Kevin Feasel

Rob Farley puzzles it out:

Back in my uni days I remember a Prolog assignment to solve “each letter represents a number” puzzles, and my solution being slow. Years later I tried it again and it worked out just fine, but by then the due date was in the past and they weren’t prepared to change my grade.

While these kinds of things can be fun (more so when there aren’t uni grades dependent on the solution), there are also times that it can be fun to rewrite some code in a way that is more intuitive, or that feels clever in a profoundly simple way.

Rob shares links to a few examples along those lines.

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