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Category: T-SQL

Window Function Execution Plans with RANGE

Published 2023-12-20 by Kevin Feasel

Hugo Kornelis continues a series on explaining the execution plans for window functions:

This is part twenty-six of the plansplaining series. And already the fourth episode about window functions. The first of those posts covered basic window functions; the second post focused on fast-track optimization for running aggregates, and the third post explained how the optimizer works around the lack of execution plan support for UNBOUNDED FOLLOWING.

But all of those were about OVER specifications that use the ROWS keyword. Let’s now look at the alternative, the RANGE keyword.

Click through to see how the various options work with RANGE. By the way, I still want range intervals, like how Postgres implements them, where you can define an interval of X days/hours/minutes/whatever rather than a specific number of rows. Maybe one of these versions…

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100 Estimated Rows

Published 2023-12-19 by Kevin Feasel

Deborah Melkin finds the optimizer in a “Dunno, here’s a guess” scenario:

A little while back, my coworker was having trouble with a query and asked me about a strange thing they were seeing in the execution plan: The estimated rows for the query was showing 100.

100 felt like an awfully specific number. And there were two scenarios I knew of where the SQL Server cardinality estimator immediately used that value – table variables and multi-statement table value functions with SQL 2016 compatibility or earlier or as part of an APPLY where interleaved execution doesn’t apply instead of a JOIN.

The statement in question didn’t use either so what was the issue?

Read on for the solution.

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Searching for a String in a SQL Server Database

Published 2023-12-15 by Kevin Feasel

Vlad Drumea is looking for a string:

This post contains a script that I’ve written and used a few times when I’ve needed to search for a string in an entire SQL Server database.

You can find more of my scripts by checking out the SQL Server Scripts category of my blog.

As a warning, this is definitely going to be slow on larger databases. But for smaller databases, it can definitely be handy.

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Advent of Code Day 4

Published 2023-12-14 by Kevin Feasel

Kevin Wilkie continues a Quixotic quest. Part 1 sets up the story:

Now we get to work with a set of numbers that our elf played and a set of winning numbers for each card. This sounds like something that SQL is meant for!

As always, we load the fun input data provided by the AoC group into our database. I actually loaded it in as 2 columns – Card and String. I’m just not a fan of throwing all of our data into one column of a table and letting it all get sorted out later.

Part 2 wraps it up:

With part 1, we just had to figure out how many times each of the winners showed up. With part 2 though, we have to jump through several hoops since we now have to determine how many cards we will end up with if we win the next series of cards for every match.

I slimmed down the table that I’m working with to only 2 columns – yes, in the real world, I would have used a view, but today was not that day.

By the way, as soon as I saw OverlyLongNamesThatNoOneCanTypeWithoutUsingIntellisense I wondered when Kevin got access to my code base. I have, on a few occasions, created punishment names, names so long that they punished the people who had to type or track them. In fairness, it wasn’t just a fit of pique, though pique was a common factor in all of those situations.

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Batch Changes in T-SQL

Published 2023-12-14 by Kevin Feasel

Erik Darling doesn’t update all the rows at once like some barbarian:

The goal of batching modifications is to accomplish large numbers of row modifications with exacerbating locking problems, and being kinder to your server’s transaction log.

There is generally an appreciable difference in transaction time in modifying 1,000 rows and modifying 10,000,000 rows. Go try it, if you don’t believe me.

Click through for more information on good ways to set up batching, including the use of the highly underrated OUTPUT ... INTO ... clause on DML statements.

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Fun with WAITFOR

Published 2023-12-14 by Kevin Feasel

Aaron Bertrand plays red light, green light:

WAITFOR is a very useful command to prevent further operations from occurring until a certain amount of time has passed (WAITFOR DELAY) or until the clock strikes a specific time (WAITFOR TIME). These commands are covered quite well (including pros and cons) in a previous tip, “SQL WAITFOR Command to Delay SQL Code Execution.”

WAITFOR DELAY is also commonly used to “let SQL Server breathe.” For example, when performing some operations in a loop, on a resource-constrained system, an artificial delay can potentially allow for more concurrency, even if it makes the intensive operation take longer.

But these commands can also be used to synchronize multiple query windows for local testing and debugging, and I thought I would share a recent example.

Click through for some of the ways you can use WAITFOR in your scripts.

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Advent of Code Day 3

Published 2023-12-12 by Kevin Feasel

Kevin Wilkie lives the struggle. Check out part one:

Then we do something very similar to what we did in Walking Through the Advent of Code Day 2 – find the digits, and the remaining text, and we’re home free!

Notice, though, that the position we grab is found at the very end. We just find the string in the line and show where it is. Except, that doesn’t always work.

And then there’s part 2:

Hopefully, by now, you’ve read my post Walking Through the Advent of Code Day 3. After looking through it, you’re probably thinking… “What have I gotten myself into? Is SQL the way to go with all of this? Can I back out now and learn a programming language that AoC can be done in “easily”?”

Click through to experience the pain or at least have a little bit of Schadenfreude in your life.

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Random Number Generation in T-SQL

Published 2023-12-11 by Kevin Feasel

Andy Yun has a method:

This is a quick blog to “document” a T-SQL technique for generating random numbers. I’ve been using this for years, but don’t use it frequently enough to have it fully memorized. So whenever I do need it, I must constantly have to go look up whenever I need to use it.

Click through for Andy’s method. This will generate random numbers based on a uniform distribution: the likelihood of getting any value in the range is equal. If you want to build out some data that approximates a normal distribution, I have a blog post for that.

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