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Category: T-SQL

T-SQL Additions to Serverless SQL Pools

Published 2020-12-21 by Kevin Feasel

Jovan Popvic lays out some of the T-SQL syntax added to serverless SQL pools in Azure Synapse Analytics:

Serverless Synapse SQL pools in Azure Synapse Analytics have a new set of features that will enable you to analyze your Azure data more efficiently. The new Transact-SQL (T-SQL) language features that you can use in serverless SQL pools are STRING_AGG, OFFSET/FETCH, PIVOT/UNPIVOT, SESSION_CONTEXT, and CONTEXT_INFO.

Old T-SQL hands will likely know what all of this does, but click through if something looks unfamiliar. All of this is available in SQL Server 2017 and later (and everything but STRING_AGG() is available going back to 2008).

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A Use Case for Recursive CTEs

Published 2020-12-17 by Kevin Feasel

Jeffin Mathew takes us through a use case for recursive common table expressions:

An individual is working in HR and wants to find out which individual is managing who. This may be for several reasons such as, they need to ask the managers on the progress of their staff and if their appraisal is coming up or is due.

Another scenario may be that the company is enrolling more staff and wants to find out the capacity of the current staff or find individuals who have not yet got anyone to manage to give them the opportunity to do so.

Click through for the solution. Often times, we see recursive CTEs show up in hierarchical queries like this. When the number of records is small, they work really well. The issue comes with scale; that’s when a different table design becomes important.

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First Thoughts on Amazon Babelfish

Published 2020-12-09 by Kevin Feasel

Ryan Booz shares some first thoughts on Amazon’s Babelfish offering:

The imputes for creating the tool is clear for AWS. Provide a way for customers to easily connect a SQL Server app to Aurora Postgres, saving big on licensing fees and reducing total cost of ownership. Assuming the tool is successful at some level, I’m sure it will provide a revenue boost for Amazon and some customers might (initially) feel a win. No harm, no foul on Amazon for leading the effort. Free markets, baby!

No matter how clever Babelfish is, however, I just can’t see how this is ultimately a win for SQL Server or PostgreSQL… or the developers that will ultimately need to support these “hybrid” apps.

I think Ryan makes good points and does hit upon the crux of the problem. I’d also say that there’s a secondary problem which Ryan hints at, but it is that a query may be sufficiently fast in one database variant but perform horridly in another. A classic example of this is a solution built on cursors in Oracle and then bringing that to T-SQL.

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Aggregate Functions in SQL Server

Published 2020-12-04 by Kevin Feasel

Hugo Kornelis takes us through the concept of aggregate functions:

SQL Server currently supports three operators that can compute aggregations: Hash Match, Stream Aggregate, and Window Aggregate. These operators all use the same basic principle of maintaining internal counters as rows are processed, so that the final value of those internal counters is the expected value.

Read on to see the full list, as well as how they operate.

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Compressing and Storing LOB Data

Published 2020-12-03 by Kevin Feasel

Randolph West hits the archives:

When we look at the several data types for storing LOB data in SQL Server, the ones we might think of first are specifically designed for storing clear text. These are VARCHAR(MAX) and NVARCHAR(MAX), which you can read up about on Microsoft Docs. They’re variable-length data types that are used to store clear text between 8,000 bytes and 2 GB. The key distinction is that NVARCHAR is for Unicode strings, which use at least two bytes per character.

Then we get VARBINARY(MAX), also for storing between 8,000 bytes and 2 GB. This data type does not make any assumptions about the stored blob’s format. You can store text, zip files, images, public key security certificates, you name it. If it can be persisted to storage, it can be stored in VARBINARY(MAX).

Read on for an example of Randolph using Gzip compression and storing XML data as binary for auditing purposes.

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JSON Basics with SQL Server

Published 2020-12-01 by Kevin Feasel

Steve Jones takes us through querying straightforward JSON data in SQL Server:

Recently I saw Jason Horner do a presentation on JSON at a user group meeting. I’ve lightly looked at JSON in some detail, and I decided to experiment with this.

All in all, I’ve been pretty happy with the syntax for JSON manipulation in T-SQL. I’m not the biggest user of JSON around, but when I’ve needed to slice or build JSON, even when I needed to build it in a certain way to emulate an old application, it has worked for me.

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Reducing CTE Re-Scans with APPLY

Published 2020-12-01 by Kevin Feasel

Daniel Hutmacher shows another good use of the APPLY operator:

You can tell by the plan why this is an inefficient query: the SQL expression in the common table expression is executed once for every time that it’s referenced in the code.

Better living through CROSS APPLY

You could store the results of the CTE in a temp table, but where’s the fun in that? Instead, why not use the CTE once, and then return four rows for each row that the CTE spits out? That’s exactly what CROSS APPLY does.

Read the whole thing and appreciate that much more all the nice things you can do with APPLY.

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GREATEST and LEAST in Azure SQL Database

Published 2020-11-27 by Kevin Feasel

Arun Sirpal shows off some missing functionality in SQL Server:

Being in the cloud does have many benefits, from lower administration to fast scaling but another “side effect” of operating in Azure SQL Database is the cloud first nature of changes. By this I basically mean new features always get pushed to Azure first before the classic on-premises version so some gems come to light.

Here is one for you. Have you ever wanted MySQL’s functinality to apply LEAST() and GREATEST() argument? Well, you can now, in Azure.

I can’t say that I would use this every day or anything, but I have felt the pain of not having it. There are workarounds, though nothing as convenient as syntax. Hopefully this shows up on-prem in the next version of SQL Server.

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Uncommon SQL Tricks

Published 2020-11-23 by Kevin Feasel

Shane O’Neill has a bandolier of SQL tricks to show off:

Recently the DBA Team Lead and I were reviewing some SQL code, and we came across some SQL that neither of us had frequently encountered before. This led to a brief watercooler moment where we shared some uncommon SQL that we had seen. Perfect blog post material, I think.

I had previously learned about ODBC date functions from Shane and also learned about CURRENT in this post, so check it out.

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