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Self-promo: Precon opportunities

January 14, 2026

I am normally not very good at promoting myself. I always forget to use the social media banners that conference organizes helpfully send me. And while I do have a list of upcoming speaking engagements on this site, I don’t really push it in your face at every opportunity. But the organizers of SeaQL 2026 pushed me. They asked me to record a video, to explain what attendees can expect when they sign up for my precon. And then, the fantastic Tonie Huizer went one step further, and created a YouTube short out of my promo video! The obvious next…

Problems purchasing videos?

January 10, 2026

Hugo Kornelis

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I started the SQLServerFast Execution Plan Video Training in 2020. At that time, I chose Vimeo as the platform to use for hosting and selling my videos. The major reason for this choice was their advertised ability to sell video access to customers across the world, so that everyone, regardless of location, can buy access to my videos and learn to read execution plans. Not in India! Two months ago, I received an email from someone who lives in India. When he tried to buy access to my videos, he received an error message: “This video is not for your…

A dark figure called "danger", armed with a knife, is chasing a running DBA.

A new experiment for 2026

January 1, 2026

Hugo Kornelis

It is January 1st, 2026. So let me first use this opportunity to wish all my readers a very good 2026, with lots of performance gains in your servers, lots of new insights into SQL Server, … but most of all, lots of love and happiness in your personal lives. Video blogging? It started when Erik Darling tempted me, even though I doubt he remembers. He has been vlogging for a long time already, and he basically dared me to try it too. I didn’t. Not at that time. But the seed was planted. During this year, I had several…

A deep dive into hash tables, part 4

December 23, 2025

Hugo Kornelis

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This is the last part of my blog series about the internals of hash tables in SQL Server. In part 1, I introduced a trick to get data returned in the order of the hash table, that I used in part 2 to gain an understanding of its internals. I then built on that in part 3 to find examples of hash collisions. With that, the discussion of the in-memory structure of a hash table is over. But what if we run out of memory and have to spill to tempdb? How is the spilled data stored on disk? I…

T-SQL Tuesday 191 – String parsing (and why I hate intelligent keys)

October 21, 2025

Hugo Kornelis

Welcome to the delayed 191st T-SQL Tuesday. Our host is, once more, Steve Jones. This time, he asks us to write about our favorite string parsing. Which is an odd thing to ask: nobody ever said “I like doing string manipulation in T-SQL”. So instead of doing what Steve asked, I will provide some background, and they show some tricks that might make the task a bit less unpleasant. Why intelligent keys are anything but intelligent I am currently most known for my performance tuning and execution plan work. But when I started working with database, I actually came from…

Black Friday 2025

October 11, 2025

Hugo Kornelis

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It’s October. Almost time for the annual Black Friday tradition, where companies prove how large their regular margins are by giving deep discounts to all their customers. Since the margin on my SQLServerFast Execution Plan Video Training is 100% (if we conveniently fail to count the hundreds of hours of labour I put in), I can also jump this bandwagon. I have done so in previous years, and by now I guess my regulars almost expect me to. So, let’s not disappoint people. Like previous years, during the entire month of November 2025, all video purchases are discounted by a…

A deep dive into hash tables, part 3

September 27, 2025

Hugo Kornelis

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Welcome back! In the previous parts, I first showed how a Hash Match (Left Outer Join) can give insight in the order of data in a hash table, and then used that trick to obtain and verify some interesting insights into the internal structure of such a table. It’s now time to see if this same trick can also be used to find hash collisions. The foundation for this part are these two conclusions from the previous parts: Unmatched rows from the left (top) input are returned bucket by bucket, with rows that are in the same bucket returned in…

T-SQL Tuesday 190 – Mastering a technical skill

September 9, 2025

Hugo Kornelis

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It’s time for T-SQL Tuesday again. Our host for edition 190 is Todd Kleinhans, and he asks us to write about mastering technical skills. I like that topic. Most of all, of course, because I spend a lot of time teaching, which is for most people the other side of mastering new skills, or improving existing skills. But also because I believe that we all live in a world of continuous learning. Those who do not learn will fall behind. Gradually at first, then ever faster. Of course, that does leave us with the choice of which technical skill to…

Video training update 2025

September 6, 2025

Hugo Kornelis

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There have not been any updates for the SQLServerFast Execution Plan Video Training for a long time. In fact, it’s already over one and a half year since the last set of videos was released! But that is not because I have been sitting still. I have, in fact, done a lot of work between then and now, even though the effects of all that work might not have been very visible. Changed plans After completing and releasing block 3 (Combining data), I started working on the next planned block, which would have been block 4 (Sorting and grouping). But…

A rather failed attempt to have AI render an image where four matches are arranged in the form of the hashtag (pound) symbol.,

A deep dive into hash tables, part 2

August 30, 2025

Hugo Kornelis

In part 1 of this series, I laid the foundation to explore the structure of the hash table, as used by the Hash Match operator, by alleging and then proving that a Hash Match (Left Outer Join) returns unmatched rows from the build input in the order in which they are stored in the hash table. This means that we can create queries on carefully curated data to gain insight in the structure of that hash table. It is now time to use that trick to actually start to explore the hash table. But not without also looking at available…

Self-promo: Precon opportunities

Problems purchasing videos?

A new experiment for 2026

A deep dive into hash tables, part 4

T-SQL Tuesday 191 – String parsing (and why I hate intelligent keys)

Black Friday 2025

A deep dive into hash tables, part 3

T-SQL Tuesday 190 – Mastering a technical skill

Video training update 2025

A deep dive into hash tables, part 2

Dr. Unknown, or how I learned to stop worrying and love the NULL

What if null if null is null null null is null?

How NOT to pass a lot of parameters

So-called “exact” numerics are not at all exact!

Curious cursor optimization options

Poor men see sharp – more cursor optimization

Bin packing part 1: Setting a baseline

Bin packing part 2: Packing it tighter

Bin packing part 3: Need for speed

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