SQLServerFast

Plansplaining, part 16. Temporal tables (part 1)

Hugo Kornelis
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Welcome to part sixteen of the plansplaining series. The first of a few posts about how temporal tables affect execution plans. In this post, I’ll build on the last four posts on data modifications, building on the more generic discussion of data modification in the previous four posts. Later posts will look at data retrieval and some specific scenarios. If you have never heard of temporal tables, I suggest reading Louis Davidson’s five part series about this feature. It seems some of the formatting has been lost in time, but the content is still good and valid. Part 1 Part…
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T-SQL Tuesday #135 – My tools to stay alive

Hugo Kornelis
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It’s February, it’s Tuesday, and we all know what that means. Time for another T-SQL Tuesday post. Our host today is Mikey Bronowski (b|t), who asks us to write about tools we use to make our jobs easier. This looked familiar. And when I checked, I found out that I did, indeed, talk about tools before. That post was specifically about tools for work. I could of course now write about new tools I discovered, or tools for other areas in my work such as presenting or recording videos. But since Mikey doesn’t restrict it to work-related tools only, I…
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T-SQL Tuesday #134 – Give me a break!

Hugo Kornelis
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The January 2021 edition of T-SQL Tuesday is hosted by James McGillivray (b|t). His question is: if you’ve been working too hard, if you’ve been spending too much time in front of a screen, what do you do to wind down? The answer to that is, for me, three-pronged. Tier 1: Do other work I work on a very varied set of activities, and I have a lot of freedom on how I choose to distribute my time: paid customer work, sometimes for multiple customers. Preparing, rehearsing, and delivering live presentations. Research and writing for the Execution Plan Reference. Authoring…
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Plansplaining, part 15. Foreign keys, part 4

Hugo Kornelis
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Welcome to part fifteen of the plansplaining series. In the three previous parts I looked at the operators and properties in an execution plan that check a modification doesn’t violate foreign key constraints. That part is done. But I’m not done with foreign keys yet. We normally expect foreign keys to throw an error on violations. But that’s actually only the default option: they can also be set to be self-correcting. This is done using the ON UPDATE and ON DELETE clauses, which provide the user with several choices on how to handle child data that would become orphaned, and…
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Plansplaining, part 14. Foreign keys, part 3

Hugo Kornelis
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Welcome to part fourteen of the plansplaining series, where I wrap up the mini-series on how simple foreign keys have huge effects on execution plans for data modifications. We already looked at inserting data in the referencing (child) table, and at deleting data from the referenced (parent) table as well as updates in the child table. We did not and will not look at deleting from the child table or inserting in the parent table: those operations can by default never violate the foreign key constraint, so no additional logic is needed. So that means there is only one thing…
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Plansplaining, part 13. Foreign keys, part 2

Hugo Kornelis
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Welcome to part thirteen of the plansplaining series. In this part I continue the exploration of how execution plans check foreign keys on data modification. In the previous part, we looked at foreign key checking when data is inserted. Inserts in the referencing (child) table can, by definition, not cause foreign key violations, so no checking is done in those cases. But for inserts in the referenced (parent) table, SQL Server needs to check that the inserted value does indeed exist. We saw how both the Nested Loops and the Merge Join operators have some specific optimizations to do that…
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Plansplaining, part 12. Foreign keys, part 1

Hugo Kornelis
5 Comments
Welcome to part twelve of the plansplaining series, where I’ll discuss foreign keys in the context of execution plans. And just to be clear, this is not about how foreign keys and other constraints can be used to simplify execution plans and speed up query executions. That is documented in so many places that I trust you already know how important those constraints are. No, today we’ll look at the extra work that SQL Server needs to do to ensure that your changes don’t violate any of your foreign key constraints. Sample tables I will use a very simple scenario…
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PASS virtual summit: thoughts, pre-con, and sessions

Hugo Kornelis
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As you probably already know by now, the 2020 edition of the PASS Summit will be held as a virtual event. Drawbacks That has drawbacks, of course. I’ve been to many PASS Summits in the past, and it’s always a great experience to be among so many fellow data professionals. To be surrounded by thousands of people that I know to have the same passion for data as I do, to face the same struggles in their daily work that I do, and to share my eagerness to absorb more information. The interactions in the hallway, the casual conversations during…
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T-SQL Tuesday #131 – Join operators simplified

Hugo Kornelis
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Another month, another T-SQL Tuesday. Our host in October, the amazing Rob Volk (b|t), wants us to explain database concepts like he is five. I like that concept. A lot. In fact, I have in the past already written similar posts, such as my explanation of SQL injection in non-technical terms to a twelve-year old grandmother. But that’s an old post, so I cannot use it for this T-SQL Tuesday. So instead, I’ll try to explain the physical join operators SQL Server supports in execution plans using a real life analogy. I don’t think a five year old would understand…
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Plansplaining, part 11. Merge plans

Hugo Kornelis
2 Comments
Welcome to part eleven of the plansplaining series. You will have noticed that this is no longer a monthly series. But when I was asked recently to provide some insight in how a MERGE statement is reflected in an execution plan, I realized that the plansplaining format works fine for this. But first a word of warning. The MERGE statement, introduced in SQL Server 2008 as an easier alternative for “delete / update / insert” logic, turned out to have issues when it was released. And now, in 2020, many of those issues still exist. So I’ll just point you…
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Hugo Kornelis

Married, father of 2 children.

Awarded 13x MVP (2006-2016; 2019-now), in the areas SQL Server and Data Platform.

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