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Category: T-SQL Tuesday

Operations Auditing with LAG() and LEAD()

Published 2023-11-15 by Kevin Feasel

Deborah Melkin builds a report query:

I’ve been doing a lot of work recently where I have long running processes where I need to have visibility on where we are during the process as well as being able to provide a report we can use to find out if there were any errors, how long each step took, and other useful information that we can use later. My solution was to create an audit log table where I simply added a row before and after each step, recording the information I had available. When the processes are done, I create a query to run over the table returning the values I want to see.

Deb also throws in the only ordered set function in SQL Server, STRING_AGG().

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Using the WINDOW Operator in SQL Server 2022

Published 2023-11-15 by Kevin Feasel

Steve Jones cuts out the duplication:

I am the host for T-SQL Tuesday this month, and I hope that a lot of people like the topic. This idea actually came to me earlier this year when I happened to see someone ask about a T-SQL problem and get an answer using a Window function. This person mentioned they hadn’t used the window function before, and I wondered how many people haven’t even tried using the OVER() clause with a window function.

Read on to see how you can use WINDOW to replicate window frames, which can be quite helpful for larger queries. It doesn’t change the performance profile but does make the code more readable.

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Good Use Cases for Window Functions

Published 2023-11-15 by Kevin Feasel

Aaron Bertrand build a list:

When I first used window functions back in SQL Server 2005, I was in awe. I had always used inefficient self-joins to calculate things like running totals, and these really didn’t scale well with size-of-data. I quickly realized you could also use them for ranks and moving averages without those cumbersome self-joins, elaborate sub-queries, or #temp tables. Those all have their place, but window functions can make them feel old-school and dirty.

I’d also recommend learning more about the APPLY operator as well, as it can, depending on the circumstances, be even more effective than window functions (combined with common table expressions) for some of the use cases.

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The Power of LAG and LEAD

Published 2023-11-15 by Kevin Feasel

Rod Edwards shows off a great use case for LAG():

I often find myself using windows functions in order to group data in wierd and wonderful ways that a simple GROUP BY can’t do… however, the example below is one I came across quite recently on my travels, I was asked to have a look at some code for optimization opportunities. And in this case, thankfully there were some.

Read on for a lengthy cursor, followed by a much less lengthy (and much faster) window function.

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T-SQL Tuesday 167 Roundup

Published 2023-10-18 by Kevin Feasel

Matthew McGiffen talks encryption:

Huge thanks to everyone who responded to my invitation to blog on Encryption and Data Protection for this month’s T-SQL Tuesday.

I got what I hoped for, which was a wide(ish) interpretation of the topic. Posts from those who are clearly advocates of encryption, and from those who have scepticism around the encryption approaches that some people take.

We’ve also got discussions about the importance of basic data governance, and the protection of intellectual property.

Read on for links to several posts on the topic of security.

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Against Transparent Data Encryption in SQL Server

Published 2023-10-11 by Kevin Feasel

Andy Yun is not a fan:

Of all of the various data protection options available to us in SQL Server, I argue that Transparent Data Encryption (aka TDE) is worthless Security Theater.

TDE encrypts your data files “at rest.” This means one cannot crack open a hex editor and just start reading your raw data. And did you know that you can use a hex editor and start reading string values right out of your MDF files? Go search on that – that’s a separate tangent you can go explore.

Read on to understand the ways in which Andy finds fault with TDE.

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A Starting Point for Data Protection

Published 2023-10-11 by Kevin Feasel

Deborah Melkin asks some questions:

If we start expanding things beyond just the technology and functionality, we can really see where the concept of data protection becomes much larger and more complex.

I admit that I’m not really up-to-speed on the technical aspects of encryption or data protection. That doesn’t fall under a lot of the work that I do. But there’s another side to data protection that’s worth talking about. It’s about knowing your data. This is where I’ve been spending a lot of my time these days.

When I ask if you know your data, I’m asking if you can answer the following questions:

Read on for some of the types of questions you’ll want to think about.

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An Overview of Transparent Data Encryption

Published 2023-10-11 by Kevin Feasel

Chad Callihan looks at one option for securing a SQL Server instance:

This month’s T-SQL Tuesday topic comes from Matthew McGiffen, who asks us to talk about encryption and protecting data in SQL Server. To read the full topic invite, click the T-SQL Tuesday logo to the right.

For this month’s invite, I thought I’d write about Transparent Data Encryption (TDE) and give a reminder about how it relates to tempdb.

Read on for Chad’s reminder.

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The Search for Extended Events Information

Published 2023-09-15 by Kevin Feasel

Grant Fritchey stays on the first page:

Here’s their paraphrased (probably badly) story:

“I was working with an organization just a few weeks back. They found that Trace was truncating the text on some queries they were trying to track. I asked them if they had tried using Extended Events. They responded: What’s that? After explaining it to them, they went away for an hour or so and came back to me saying that had fixed the problem.”

We all smiled and chuckled. But then it struck me. This wasn’t a case of someone who simply had a lot more experience and understanding of Profiler/Trace, so they preferred to use it. They had literally never heard of Extended Events.

Why?

This led Grant to perform some search engine shenanigans and what he found was curious. A couple of points with search engines, though:

  • Search engine results will differ based on your location (IP address) and whether you are signed in or not. Google is particularly selective about this stuff. It might also affect Bing, but let’s face it: if you’re using Bing to search for anything other than images, you’ve already resigned yourself to failure.
  • In my case, a search for “extended events” (without quotation marks) did show quite a few pages which I’d consider reasonable for the topic: a Microsoft Learn quickstart article on using extended events, Brent Ozar’s extended events material, a SQL Shack article on the topic, etc. A good number of these links are content from the past 5 years, as well.
  • Grant mentions the “page 1” effect in search engines, and he’s absolutely right. The vast majority of people performing a search never leave the first page of results. This is part of why Google went to an infinite scrolling approach rather than showing explicit numbered pages.
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