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Category: T-SQL

Modulus Computations on Large Numbers

Published 2022-09-27 by Kevin Feasel

Daniel Hutmacher does the math:

The modulus is the remainder of a division of two integers*. Suppose you divide 12 by 4, the result is 3. But divide 11 by 4, and the result is 2.75. This could also be expressed by saying that 11/4 is 2 with a remainder of 3. Computing that 3 is the work of the modulo operator, which in T-SQL is represented by the % operator.

Let’s explore how to compute the modulus of large numbers in SQL Server, and how this is useful in the real world.

Daniel’s example includes IBAN validation, though I think he’s secretly working on breaking asymmetric encryption…

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Careful Batching

Published 2022-09-22 by Kevin Feasel

Michael J. Swart follows up on an older post:

When I wrote Take Care When Scripting Batches, I wanted to guard against a common pitfall when implementing a batching solution (n-squared performance). I suggested a way to be careful. But I knew that my solution was not going to be universally applicable to everyone else’s situation. So I wrote that post with a focus on how to evaluate candidate solutions.

But we developers love recipes for problem solving. I wish it was the case that for whatever kind of problem you got, you just stick the right formula in and problem solved. But unfortunately everyone’s situation is different and the majority of questions I get are of the form “What about my situation?” I’m afraid that without extra details, the best advice remains to do the work to set up the tests and find out for yourself.

Definitely read the original article first. My normal approach is the naive + index method, so I’ll have to try out Michael’s method as well next time I need to delete a chunk of records.

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Deleting Rows in Order

Published 2022-09-16 by Kevin Feasel

David Fowler understand the order of things:

This was an interesting question that I was asked yesterday and something that I’d never really thought of before. Can you delete the top x number of rows based on an ORDER BY?

Why would you want to do that? Well let’s just assume that we have a ‘people’ table and some strange bug in the application has cause the need to delete the top 10 oldest females for whatever reason (I know, it’s very contrived example and not the situation that my colleague was facing but it’ll do to illustrate the point).

Click through for one way which doesn’t work and two ways which do.

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Date Calculation (and Calendar Tables) in SQL Server

Published 2022-09-15 by Kevin Feasel

Aaron Bertrand makes the case for calendar tables:

In a previous tip, Simplify Date Period Calculations in SQL Server, I described how to easily calculate certain dates, like the first day of a given month, quarter, or year. Another common scenario is trying to find the last weekday of the month, or the nth Monday or Wednesday. In this tip, I will show ways to simplify these calculations, both with and without a calendar table.

Click through for Aaron’s approach to the problem. I have a blunter approach in creating an expansive calendar table and using it. You do the heavy lifting one time and are good for life on that server.

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IS [NOT] DISTINCT FROM

Published 2022-09-14 by Kevin Feasel

Louis Davidson likes a new operator in SQL Server 2022:

The MOST exciting change from a T-SQL standpoint is: IS NOT DISTINCT FROM. This feature solves an age-old issue for T-SQL programmers and is worth its weight in gold. It is basically an equals comparison operator like =, but treats NULL as an individual value. Unlike =, this new operator returns only TRUE or FALSE, but not UNKNOWN. Writing queries that compare to values that can contain NULL is tedious, mostly because of code like the following:

Louis is quite happy here. I like the fact that the syntax is here, though I’d be concerned about performance—the syntax is nicer but you can run into the same performance issues as you’d have with “NULL or match” type queries.

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Compacting Window Function Definitions

Published 2022-09-14 by Kevin Feasel

Rob Farley like a syntax change:

This was fine, but it did start to become a little cumbersome.

Enter SQL Server 2022. Not only do we get the ability to ignore nulls now, making it easy to get the last non-null value from a list, but we also get a WINDOW clause – part of the SELECT query itself, dropping in between the HAVING clause and the ORDER BY clause, allowing us to predefine those OVER clause segments.

Read on for the full scope of Rob’s thoughts.

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Working with CROSS APPLY

Published 2022-09-13 by Kevin Feasel

Paul Randal takes us through one of my favorite operators:

Introduced by Microsoft in SQL Server 2005, SQL CROSS APPLY allows values to be passed from a table or view into a user-defined function or subquery. This tutorial will cover the incredibly useful and flexible APPLY operator, such as how the CROSS APPLY and OUTER APPLY operators work, how they’re like the INNER and LEFT OUTER JOIN, and give you some examples of both. All the examples use the AdventureWorks example database.

Later in the article, I’ll also discuss a highly pervasive SQL Server performance problem—one I still encounter with customers on a weekly basis. This problem is related to using the APPLY operator against a specific type of user-defined function. It’s so problematic and can overwhelm tempdb, bringing your SQL Server instance to a crawl!

If you’re not too familiar with APPLY in its two forms, read the whole thing.

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Building UNPIVOT Syntax

Published 2022-09-08 by Kevin Feasel

Michael J. Swart has a function:

Just like PIVOT syntax, UNPIVOT syntax is hard to remember.
When I can, I prefer to pivot and unpivot in the application, but here’s a function I use sometimes when I want don’t want to scroll horizontally in SSMS.

Click through for the function. This is an area where I wish there was built-in * logic for PIVOT and UNPIVOT. Or at least a “Select all columns but the following” as that would make things easier.

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FizzBuzz in SQL

Published 2022-09-08 by Kevin Feasel

Cathrine Wilhelmsen does some modulo division:

This week, my coworkers and I were given a fun challenge. Using any tool or language, solve FizzBuzz! Then present and explain the solution to the rest of the team. This was a fun challenge because our team is a mix of junior-to-senior developers and data professionals, working with everything from SQL to Python to C# to DAX to PowerShell. Those who had never solved FizzBuzz before got the chance to do so, while those who had already solved it got the chance to try again using a different tool or language.

Read on for Cathrine’s solution using a tally table. This classic variant of FizzBuzz is pretty easy to do in T-SQL; building the numbers table is the trickiest part.

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