T-SQL on Andy M Mallon - AM²

T-SQL Tuesday: The last ticket I closed

Tue, 13 Feb 2024 12:41:20 -0500

For this month's T-SQL Tuesday, Brent Ozar (blog|Instagram) asks us to describe the most recent ticket we closed.

“We had a pretty significant wait spike…”

The literal last ticket I closed was “please run this script in production…”, and I don’t think it would be a very interesting blog post to talk about how I copy & pasted a query into SSMS, so let’s talk about a recent ticket instead, from the last couple of weeks.

Using OPENJSON, can't get results to GROUP BY

Sat, 24 Dec 2022 18:35:57 -0500

Question

I'm passing a JSON string to a stored procedure in order to insert warehouse inventory.

Sometimes, there will be multiple line items with the same product, going to the same shelf, on the same pallet (LPN), with the same date. I would like to aggregate those into one line in the table.

How do I prevent a trigger from firing for one process?

Tue, 08 Mar 2022 09:00:16 -0500

I recently saw a question on DBA Stack Exchange (it has since been deleted by the author), who had a “special process” that ran regularly, and as part of that process, they disabled the trigger, did some stuff, and re-enabled it. During that process, the step that disables the trigger would deadlock, and cause problems. So the asker was wondering how to catch & handle the deadlock during the DISABLE TRIGGER step.

Querying SERVERPROPERTY() and DATABASEPROPERTYEX() from a view (without knowing magic)

Fri, 17 Dec 2021 11:11:50 -0500

Elphaba the pup is growing up! I'm not going to beat around the bush. I hate the `SERVERPROPERTY()` and `DATABASEPROPERTYEX()` system functions.

Loathing

The thing I hate the most about these two functions is that you need to know the right magic spells to make them work. Let’s look at SERVERPROPERTY() first. The syntax for the function is SERVERPROPERTY( ‘propertyname’ ), which is easy enough syntax, but the list of values for propertyname isn’t discoverable from SQL Server metadata, DMVs, or even IntelliSense. Instead, I need to check the docs for the list of allowable values. These property names are essentially magic words, and I need to check my spell book to make sure I get it right.

What time is it in Oz?

Tue, 05 Oct 2021 15:54:03 -0400

This is our puppy Elphaba. She's from Oz...No, the other Oz. She's popular.

There was a recent post on Database Administrators, where there was some confusion over Daylight Saving Time(DST) in Australian timezones. Let’s be honest though–timezones are confusing, especially when DST comes into play. Arizona Time doesn’t observe Daylight Saving Time, so sometimes it’s the same as Mountain Time, and sometimes it’s Pacific Time.

Stop using sp_hexadecimal & sp_help_revlogin

Tue, 06 Jul 2021 09:00:52 -0400

Caterpillars transform into beautiful butterflies to realize their full self, much in the same way CONVERT() changes binary into beautiful hexadecimal strings.

Since I started at Stack Overflow, I’ve had the chance to see some of the interesting challenges with running our databases at our scale.

Find the SQL Server service account with sys.dm_server_services

Tue, 12 May 2020 09:00:56 -0400

This is Callie. She has nothing to do with DMVs, but isn't she cute?!

SQL Server 2005 introduced Dynamic Management Views(DMVs). Technically, there are both views & functions–DMVs & DMFs, but colloquially they’re often simply referred to as just “DMVs”. DMVs simply return information about the state of the server or database and can be used for monitoring and troubleshooting of server/database health & performance.

Making non-SARGable queries seek, without changing the query

Wed, 06 May 2020 08:36:27 -0400

We’ve all been there. You’ve got a query where the JOIN or WHERE predicate is not SARGable. You’ve read about how this can be a problem, and how bad it is for performance.

Alas, you cannot change the query. Sometimes this reason is political, sometimes it’s because you’ve got a third-party app and simply don’t have access to the code. But you do have access to the database…

Fixing tempdb: Growing, shrinking, and removing data files

Tue, 21 Apr 2020 09:00:37 -0400

Dropping tempdb files like they're hot

I recently came across a server where tempdb was breaking all the rules.

Data files were all different sizes. I want all data files to be the same size so that proportional fill uses them evenly.
There were 10 tempdb files, with 8 files on a dedicated disk, and 2 on a slower disk shared with other data files. And free space was sky high, so the extra files aren't needed anymore! (They were probably added to fix a short-term emergency, and never cleaned up.)
The log file was tiny, and didn't have room to grow. For a 500GB tempdb, the log file was only 4GB!

Three fixes

There are three problems I’ve got to fix. I need to (1) remove those two extra files, (2) grow the tempdb log file, and (3) even out the size of the data files (and shrink them a little to make room for the larger log file. We’re going to tackle these in the reverse order than I listed them–partially out of necessity, and partially because it’s going to be easier.

When STRING_SPLIT() falls short

Fri, 20 Mar 2020 10:00:54 -0400

Aaron attempting a STONE_SPLIT at a recent curling competition. This morning, my friend Aaron Bertrand (blog|twitter) posted a plea for help with STRING_SPLIT() improvements. I'm very much in Aaron's corner on this, having written about the olden days myself.

Why `STRING_SPLIT()` is supposed to be awesome

CLR was fast, but inaccessible to many DBAs. XML was almost as good, but ugh, XML. And multi-statement table valued functions are evil but prevalent.

STRING_SPLIT() promised to be both super fast, and lift the code maintenance problem for DBAs who don’t know .NET and struggle with the crazy XML syntax.

Blocking with OBJECT_NAME()

Tue, 24 Dec 2019 10:38:36 -0500

Doggos increase blog readership by 140%. 14/10. They are good doggos.

As a DBA, you probably use the OBJECT_NAME() function quite a bit. I know I do. If you aren’t familiar with it, you can read the documentation if you want, but it’s a pretty straightforward function that converts object IDs into object names.

Testing as another user...without their password

Wed, 18 Dec 2019 11:50:35 -0500

This guy doesn't have Elvis's password and is still able to impersonate him. As a DBA or SQL Developer, you've surely encountered a scenario where something worked for you, but not for another user. DBAs usually are part of the sysadmin role, or have a collection of powerful permissions. If I run code as myself, I will *never* have permissions problems because my account is sysadmin. If I want to ensure permissions are correct, I need to run the code as the less-privileged account.

Can you try now?

I honestly don’t think there is a more frustrating experience than getting into the feedback loop of making a permission change, and asking the user if it works, and when it doesn’t work, you try another change, and ask them to try again, and when it doesn’t work, you try another change, and ask them to try again, and when it doesn’t work, you try another change, and ask them to try again, and when it doesn’t work, you try another change, and ask them to try again…

Changing a column from int to bigint, without downtime

Wed, 11 Dec 2019 08:00:41 -0500

Changing a column from int to bigint has gotten a lot easier since I started working on SQL Server back at the turn of the century. SQL Server 2016 introduced the ability to do ALTER TABLE...ALTER COLUMN as an online operation using the WITH (ONLINE=ON) syntax in Enterprise Edition. This wonderful syntax now allows you to alter a column from int to bigint without causing major blocking. The int to bigint conversion is one of the most popular data type changes I see–A developer inevitably creates the table thinking they will never have more than 2 billion rows… then some years or months later 2 billion becomes a reality.

How to create date buckets in T-SQL

Mon, 28 Oct 2019 10:00:47 -0400

I was fiddling around with some data, looking at making a quick aging report. I probably should have reached for Power BI Desktop, but sometimes I can be stubborn, and I wanted to get my T-SQL to work–if nothing else to figure out how to make it work.

Why does ALTER let me DROP?

Wed, 28 Aug 2019 09:00:19 -0400

I was recently chatting with a coworker, discussing why there is no discrete DROP permission for tables, procedures, etc. The conversation actually came from a #SQLHelp question on SQL Slack that was asked along the lines of “What if I want to let a user CREATE and ALTER objects, but not DROP them?”

Year 4: May 2017 - May 2018

Tue, 21 May 2019 08:30:21 -0400

In Year Three, I had a pretty big year. I kind of felt like I had peaked. I had received the Community Influencer of the Year Award and Microsoft MVP Award. Where do you go from there? Mostly, I just wanted to keep up what I was doing, and keep sharing what I was doing.

Code to purge data based on creation date

Thu, 04 Apr 2019 08:30:16 -0400

Only one thing can spark more joy than cleaning up old data. Doggos. Yesterday, I talked about batching deletes, and the day before I talked about how much I like to delete data, and why it's necessary to do it, despite being a data packrat.

Today, let’s look at just one scenario, and how I like to handle it. In my experience, this is one of the most common purge requirements (and probably the easiest), so first, let’s look at the business requirements.

Purging data with batched deletes

Wed, 03 Apr 2019 08:30:13 -0400

This person understands that batching deletes can be helpful. Yesterday, I wrote about the importance of planning your data purges. Today, let's look at the simplest requirement for purging data: Keep data for X days after it's created. There are tons of cases where this is the rule. Log data, telemetry data, even transactional data is often retained based on X days since it is created.

Given how common this scenario is, let’s talk in a bit more detail about I like to go about deleting it. Deleting data is easy, right? DELETE t FROM dbo.Transactions AS t WHERE CreateDate <= DATEADD(dd,-90,GETDATE());

The thrill of purging old data

Tue, 02 Apr 2019 09:00:54 -0400

I get a thrill from roller coasters, but for some people it just makes them purge their lunch.

DBAs & Data professionals tend to be digital pack rats. My personal Google Drive is filled with random files that I refused to part with–even though it’s of questionable value. I lament that I do not have a copy of every paper I typed in high school or college–and I envy those who do. You never know when you’ll need notes from that meeting 6 years ago, or when you’ll need that funny GIF you created for an inside joke you no longer remember.

TSQL Tuesday #99: Tabs vs Spaces

Tue, 13 Feb 2018 07:02:30 -0500

It’s T-SQL Tuesday, the blog party that SQL Server expert Adam Machanic (blog|twitter) started. This month’s episode is hosted by Aaron Bertrand (blog | twitter). The topic: Dealer's Choice (Door Number 2: Bad Habits)

When I was a kid, Choose Your Own Adventure books were overwhelming because I wanted to explore every possible option–some things never change. This month for T-SQL Tuesday, Aaron offers two blogging options and I’ve chosen to do both. “Door Number 1” is a challenge to write about what you do in your free time, inspired by Drew Furgiuele’s #sqlibirum post. That blog post is over here. This post is for the “Door Number 2” option is to talk about his Bad Habits series–I’ve opted to bring up a topic Aaron hasn’t blogged about: tabs vs spaces.

Parsing file names from paths using T-SQL

Wed, 17 Jan 2018 07:00:40 -0500

These files are way neater than the ones on my laptop.

SQL Server is great at a lot of things. I spend a lot of time blogging about all the cool things that SQL Server does. But (you knew there was a “but”, didn’t you) SQL Server isn’t great at everything. Lets write about something that SQL Server is bad at.

Finding active transactions

Tue, 02 Jan 2018 09:04:07 -0500

Confessions of a carbaholic: When I start thinking about `ROLLBACK`, I start thinking about rolls.

Have you ever forgot to commit a transaction? Maybe you’ve even left for lunch and caused a problem while you were gone. Uncommitted transactions can cause all sorts of problems–not just blocking, but it can affect your Availability Groups & Mirroring, your TempDB version store if you’re using one of the snapshot isolation levels.

Finding the Leader Blocker

Thu, 26 Oct 2017 23:55:09 -0400

Who's at the front of the line blocking all the traffic?

During the course of normal processing in a database, blocking happens. Blocking is “by design” because your database is on ACID. In an OLTP database, most of your transactions are short in duration, so we expect blocking to also be short in duration. If blocking occurs for a long time, this can cause problems.

Multi-Statement TVFs in Dynamics CRM

Tue, 22 Aug 2017 13:19:18 -0400

If you’re familiar with supporting the database behind Microsoft Dynamics CRM, you probably know that it’s not the fastest-performing database. Honestly, that shouldn’t be a surprise–it’s not designed to be a screaming-fast database. It’s designed to be a flexible database. Most Customer Relationship Management (CRM) systems are designed to be flexible so that they can meet the needs of many businesses in many industries with vastly different business requirements. They put those requirements ahead of database performance. That’s probably smart business, but I’m not a business person–I’m a database person. My experience with Dynamics CRM is when people come to me and say

What’s wrong with DELETE EXISTS?

Fri, 30 Jun 2017 14:26:41 -0400

I loved playing Number Munchers on my Apple IIc

This morning, when I logged into Twitter, the tweet at the top of my timeline was from Shane O’Neill (blog|twitter). It was to his blog post, Shane, What’s wrong with DELETE EXISTS?. It’s not that unusual that Shane would talk to himself in the third person, but I was intrigued by the title.

Will a SELECT . . . INTO use short-circuit evaluation for a COALESCE?

Tue, 02 Aug 2016 14:45:55 -0400

Question

I'm building a stored proc that can take in two separate values that each can be used to identify a single record. One of these values may be null.

My logic is as follows: if IN_ORDER_ID is not NULL, save it to V_ORDER_ID. If it is NULL, then retrieve ORDER_ID with a query and save that to V_ORDER_ID. V_ORDER_ID is then used in the rest of the procedure.

Add-Equals operator

Tue, 24 May 2016 10:00:19 -0400

Shortcuts & tips from an Impatient DBA

This series of short posts will demonstrate some lesser-known features, keyboard shortcuts, and other tips that make my day as a DBA more productive. None of these are groundbreaking super-secret features–they are the little things that I do as part of my daily work that make me more efficient.

How to shrink a database in 4 easy steps

Thu, 28 Apr 2016 11:00:22 -0400

I pity the fool who needs to shrink his database!

It’s a really common question: “How do I shrink my database?” Luckily, there’s also a really common answer: “Don’t.”

…but what if you really have to?

Perhaps you just implemented data compression, and have 60% free space in your database. Perhaps you just deleted a bunch of old data, and have significant free space in your database. There are a handful of scenarios where you have free space in the database, you’ll never use it, and you need to shrink. Just don’t make a habit of it.

CONVERT() to float using scientific notation

Wed, 20 Apr 2016 10:57:01 -0400

Someone posted to #sqlhelp on Twitter, asking the following: “Wondered if anyone could enlighten me as to why ISNUMERIC(‘7d8’) returns 1?”

Sure enough, SELECT ISNUMERIC('7d8') returns a 1.

WTF? d isn’t numeric!

OK, sure, if you say “seven-dee-eight” out loud it sounds like a number, but “d” is a letter, not a number.

Decoding sql_handle

Mon, 29 Feb 2016 10:05:54 -0500

If you’ve ever looked at sys.sysprocesses or sys.dm_exec_requests (or a number of other DMVs), you’ve noticed there is a column called “sql_handle” that contains some binary gobbledygook. Books Online gives the (un)helpful definition as “Hash map of the SQL text of the request.”

sp_WhoIsActive

In the context of currently-running processes, most people decode sql_handle with Adam Machanic’s (blog|twitter) sp_WhoIsActive. It’s really easy & straightforward–if you’re not familiar with Adam’s utility, download it and check it out. My friend Mike Kane (blog|twitter) has an interesting post on parameter combinations he regularly uses when using sp_WhoIsActive.

RECONFIGURE—When to use WITH OVERRIDE?

Tue, 17 Nov 2015 11:00:19 -0500

When you’re using sp_configure to change a system configuration, you have to run a RECONFIGURE to finalize your change. You even get the helpful output that reminds you to run RECONFIGURE:

Configuration option 'max degree of parallelism' changed from 0 to 1. 
Run the RECONFIGURE statement to install.

There are many places online with code samples (Books Online, blog posts, vendor documentation, etc) that actually use the additional “RECONFIGURE WITH OVERRIDE” syntax: Here. Here. Here. There are even posts that switch between including “WITH OVERRIDE” and not including it Here.

Converting delimited values to a table (efficiently?)

Tue, 21 Apr 2015 15:33:00 -0400

This is a pretty common problem. I think it’s a question every developer has asked at one time or another: “I want to pass in a comma-separated list of values, then convert it into a table."

Every company I’ve ever worked for has had a function that does this. Everyone does it differently. It’s never efficient. I’ve seen it done in CLR, I’ve seen it done as a multi-statement table-valued user-defined function (which we all know is the devil’s work). The CLR works, but it’s a black-box to the average DBA or SQL developer. The multi-statement TVF performs terribly, but has never been used heavily enough to make it to the top of my tuning list.

This morning, I saw Pinal Dave (twitter|blog) post on his blog about this topic, and he used a really elegant XML-based solution. It’s one of those solutions that’s so simple, it’s incredibly hard.

When I got to my desk this morning, I immediately wrapped Pinal’s code into a function that was backwards compatible to a multi-statement TVF version and performance tested them head-to-head.

Here’s my function definition:

sp_executesql with output parameters

Thu, 22 Jan 2015 20:05:00 -0500

One of my coworkers asked me about output parameters from dynamic SQL today. I pointed him at sp_executesql, which allows for passing parameters into or out of dynamic SQL. The syntax can be confusing at first blush (especially for a new DBA or developer), but it’s really pretty straightforward, easy, and useful.

T-SQL on Andy M Mallon - AM²

T-SQL Tuesday: The last ticket I closed

“We had a pretty significant wait spike…”

Using OPENJSON, can't get results to GROUP BY

Question

How do I prevent a trigger from firing for one process?

Querying SERVERPROPERTY() and DATABASEPROPERTYEX() from a view (without knowing magic)

Loathing

What time is it in Oz?

Stop using sp_hexadecimal & sp_help_revlogin

Find the SQL Server service account with sys.dm_server_services

Making non-SARGable queries seek, without changing the query

Fixing tempdb: Growing, shrinking, and removing data files

Three fixes

When STRING_SPLIT() falls short

Why STRING_SPLIT() is supposed to be awesome

Blocking with OBJECT_NAME()

Testing as another user...without their password

Can you try now?

Can you try now?

Can you try now?

Can you try now?

Changing a column from int to bigint, without downtime

How to create date buckets in T-SQL

Why does ALTER let me DROP?

Year 4: May 2017 - May 2018

Code to purge data based on creation date

Purging data with batched deletes

The thrill of purging old data

TSQL Tuesday #99: Tabs vs Spaces

Parsing file names from paths using T-SQL

Finding active transactions

Finding the Leader Blocker

Multi-Statement TVFs in Dynamics CRM

What’s wrong with DELETE EXISTS?

Will a SELECT . . . INTO use short-circuit evaluation for a COALESCE?

Question

Add-Equals operator

Shortcuts & tips from an Impatient DBA

How to shrink a database in 4 easy steps

…but what if you really have to?

CONVERT() to float using scientific notation

WTF? d isn’t numeric!

Decoding sql_handle

sp_WhoIsActive

RECONFIGURE—When to use WITH OVERRIDE?

Converting delimited values to a table (efficiently?)

sp_executesql with output parameters

Why `STRING_SPLIT()` is supposed to be awesome