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Curated SQL Posts

Alternatives to GREATEST() and LEAST()

Published 2021-04-19 by Kevin Feasel

Mike Scalise has an alternative to using the GREATEST() and LEAST() functions in SQL Server:

As of 4/14/21, Microsoft has officially announced that the GREATEST and LEAST functions are in Azure SQL Database and SQL Managed Instance. Unofficially, it seems they had silently included these functions in at least (no pun intended) SQL Managed Instance several months prior. In any case, here we are today with official Microsoft documentation on GREATEST and LEAST. This is all great news. What’s also great is that, in their statement, Microsoft stated they would be including these two functions in the next version of SQL Server.

But what about all of us on SQL Server 2019 and prior? Fortunately, there’s a way to mimic these two functions in your queries using a correlated subquery in the SELECT clause.

Click through for examples. This is a bit different from getting the largest or smallest value in a window, which you can do with MIN(val) OVER () or MAX(val) OVER (). But I’m looking forward to seeing GREATEST() and LEAST() in the box product.

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Improving Dataflow Performance in Power BI

Published 2021-04-19 by Kevin Feasel

Chris Webb shows how you can improve dataflow performance in Power BI after switching to a Premium Per User model:

Over the years I have written a lot about Power BI/Power Query performance but it has always been in the context of loading data direct into datasets, not dataflows. A lot of cool things have been happening in dataflows recently, though, and now that Premium Per User has made Premium features to a much wider audience I thought it would be interesting to look at an example of how PPU can help dataflow performance and specifically how and when the Enhanced Compute Engine can make dataflow refresh faster.

Click through for some interesting findings.

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Check Those Feature Distributions

Published 2021-04-16 by Kevin Feasel

Antoine Rebecq shares a warning:

I was recently working on a cool dataset that looked unusually friendly. It was tidy, neat, interesting… the kind of things that you rarely encounter in the wild! My goal was to build a super simple predictor for one of the features. However, I kept getting poor results and at first couldn’t figure out what was happening.

There’s some good, practical advice in there, so check it out. H/T R-Bloggers

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Conditional Expressions in Elasticsearch

Published 2021-04-16 by Kevin Feasel

The Hadoop in Real World team explains how to perform OR, AND, and NOT operations in Elasticsearch queries:

We can specify conditional expressions like OR, AND using the Query expression during search in Elasticsearch.

We have an index named account and in the index we have details of account owners including their name, address, age, sex, employer etc.

Let’s search the documents with AGE=25 and STATE IN (‘ca’, ‘ny’) in the index.

As a spoiler, it’s not as easy as using OR, AND, and NOT, though there are synonyms.

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Automating Workflows in Azure DevOps with Logic Apps

Published 2021-04-16 by Kevin Feasel

Elie Bou Issa does some no-code automation:

Azure Logic Apps is a cloud service to help you schedule, automate, and orchestrate tasks and workflows between apps and across enterprises and organizations. A Logic App can be built using the Azure portal, or infrastructure as code.

By the end of this article, you will have a good understanding of leveraging a Logic App for Azure DevOps to automate the create of work items, in addition to creating an automated approval-based workflow using Office 365.

Click through for the demo. This is useful on its own, especially with non-technical product managers, but you can extend the use of Logic Apps quite a bit and automate more work without writing much code.

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Using AD Authentication on Linux when Connecting to SQL Server

Published 2021-04-16 by Kevin Feasel

Daniel Hutmacher shares some hard-earned wisdom:

I’m a complete beginner at Linux, so I should preface this post with the fact that these are my humble notes after hours of pulling my hair. It’s not really a fully-fledged how-to article, and there are lot of things I’m not covering. But I figured it may help someone out there at some point.

Also, different Linux distros and versions will behave differently, so your mileage will most likely vary.

For the purposes of this post, I’m on Red Hat Enterprise 8.3.

Note that this is using a Linux-based client, rather than talking about SQL Server on Linux.

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Inserted and Deleted Scans

Published 2021-04-16 by Kevin Feasel

Hugo Kornelis has a two-parter for us. First up is the inserted scan operator:

The Inserted Scan operator is only found in execution plans for code in triggers. It is used for queries that read data from the inserted pseudo-table. Its counterpart, Deleted Scan, reads from the deleted pseudo-table.

This pseudo-table contains a copy of all the rows that were inserted in AFTER INSERT triggers, or the new content of the data in all affected rows in AFTER UPDATE triggers. In INSTEAD OF INSERT or INSTEAD OF UPDATE triggers, the data in the inserted pseudo-table is the data that would have been inserted, or the data as it would have been after the update. In AFTER DELETE and INSTEAD OF DELETE triggers, using the inserted pseudo-table is allowed but returns no data.

Then, the deleted scan:

This pseudo-table contains a copy of all rows that has just been deleted in AFTER DELETE triggers, or the original data of all affected rows in AFTER UPDATE triggers. In INSTEAD OF DELETE or INSTEAD OF UPDATE triggers, the data in the deleted pseudo-table is the current data in the rows that would have been deleted or updated. In AFTER INSERT and INSTEAD OF INSERT triggers, using the deleted pseudo-table is allowed but returns no data.

Click through to see how they work.

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Index Unions

Published 2021-04-16 by Kevin Feasel

Erik Darling continues a multi-state indexing spree:

Index union is a little bit different from index intersection. Rather than joining two indexes together, their result sets are concatenated together.

Just like you’d see if you wrote a query with union or union all. Crazy, huh?

As with index intersection, the optimizer has a choice between concatenation and merge join concatenation, and lookups back to the clustered index are possible.

These I see even less commonly than index intersections—so often, the optimizer decides simply to scan one index and the solution is to break the queries out into two with UNION ALL.

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