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Category: T-SQL

Things You Can Do with Random Values

Published 2021-10-14 by Kevin Feasel

Andy Yun shows off some random skills:

First, there are times where you need multiple random numbers. Simply using multiple iterations of RAND() in a single statement won’t cut it, as you need to vary the seed. So I keep this snippet handy for when I need a bunch of random values in a single statement:

Click through for that as well as two more uses of RANDOM(). This is my reminder that RANDOM() generates data across a uniform distribution (every value in the range is equally likely to be chosen), making it great for these sorts of experiments but can look weird by itself if you’d expect non-uniform distributions of the data. For that, you would need some distributional trickery—though frankly, between the uniform and normal distributions, you’ve probably covered about 95-99% of test dataset needs.

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15 Short Code Snippets

Published 2021-10-14 by Kevin Feasel

Chad Baldwin goes the extra mile:

I’m excited that this will be my first time participating in a T-SQL Tuesday topic!

Most of my time is spent writing T-SQL, PowerShell and working in the PowerShell terminal, so that’s how I’ll split the post up.

I had to cut it short otherwise this post would be a mile long. If you’re interested in seeing more quick tricks, SQL Prompt snippets, etc, please leave a comment and let me know and I can do a Part 2 in the future.

Click through for a baker’s dozen plus a couple spares.

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Adding Debug Logic to T-SQL Procedures

Published 2021-10-13 by Kevin Feasel

Deborah Melkin does not take kindly to bugs:

I often find that I have to write complicated stored procedures where I need to check things as I go along. My go-to for using this snippet is when I write stored procedures that use dynamic SQL. You’d be surprised (or not) at how often I have had to do this over the years. There’s been functionality where the user gets to choose the columns being used, rewriting ORM data layer “catch-all” queries to improve performance, and cross database queries where the name of the database may not be the standard name (think development and QA databases living on the same SQL instance.)

Click through for an example of where the @Debug parameter pays off. My recollection was that, for really long NVARCHAR(MAX) strings, running PRINT by itself might cut off the code after ~4000 characters, but that could be a historical recollection.

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Repurposing Helpful Scripts

Published 2021-10-13 by Kevin Feasel

Deepthi Goguri re-shares some helpful scripts:

For the past couple of years as a DBA, I migrated several databases and used many handy scripts that helped me made my work easier. These scripts may be simple but if you have a migration project involving several SQL Servers with some hundreds of databases, test and production database migrations becomes tedious. I would like to share some of then here which you might already known them very well.

Click through for three scripts.

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Short Query Store Queries

Published 2021-10-13 by Kevin Feasel

Mala Mahadevan has a few short-ish Query Store scripts for us:

I use Query Store a lot where I work – and I’d like to share queries I use on Query Store DMVs that I find incredibly useful.

My favorite is one below, which I use to see stored procedure duration. It comes with other information including plan id, start and end time – all of us help me see red flags right away if there is any query not performing as well as it should.

Click through for that script as well as two more.

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Searching T-SQL Objects

Published 2021-10-12 by Kevin Feasel

Rob Farley has a quick script to find references in SQL Server:

As a consultant, the kind of work that I do from customer to customer can change a bit. Sometimes I’m reviewing people’s environments; sometimes I’m performance tuning; sometimes I’m developing code or reports or cubes; sometimes I’m writing T-SQL, but it’s often DAX or PowerShell.

Click through for a quick script to search modules for a particular string.

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Optimizing for Mediocre

Published 2021-10-11 by Kevin Feasel

Erik Darling points out an issue with some approaches to preventing parameter sniffing problems in queries:

Despite the many metric tons of blog posts warning people about this stuff, I still see many local variables and optimize for unknown hints. As a solution to parameter sniffing, it’s probably the best choice 1/1000th of the time. I still end up having to fix the other 999/1000 times, though.

In this post, I want to show you how using either optimize for unknown or local variables makes my job — and the job of anyone trying to fix this stuff — harder than it should be.

Click through for two methods, both of which end up being the wrong answer.

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Value Comparisons with Nullable Columns

Published 2021-10-11 by Kevin Feasel

Chad Baldwin wants to check if rows exist before inserting:

I haven’t posted in a while, so I thought I would throw a quick one together to hopefully restart the habit of writing and posting on a regular basis.

One of my first blog posts covered how to only update rows that changed. In that post, I described a popular method that uses EXISTS and EXCEPT to find rows that had changed while also implicitly handling NULL values.

Click through for two types of technique, one for non-nullable data and one which can include NULL.

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Foreign Keys and Delete Operations

Published 2021-10-08 by Kevin Feasel

Kenneth Fisher takes us through a case of deleting rows:

Deleting rows from a table is a pretty simple task right? Not always. Foreign keys, while providing a ton of benefits, do make deletes a bit more complicated.

Click through for an example of this, as well as a quick discussion of cascading deletes, which sound really useful until you make a big mistake. The other problem with cascading deletes is, even if you do intend to delete everything noted, the process is a lot slower than what you can do in batches, and you’re liable to increase the size of your transaction log file to boot.

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