Category: Syntax

Lukas Vileikis shows off a bit of ANSI SQL syntax:

When the need to deal with NULL values arises, multiple queries come onto the scene. The SQL COALESCE function is one of them. In simple terms, the SQL COALESCE function is a ‘fallback’ mechanism for missing data. Its only task is to return the first non-NULL value from a list of values.

I used to be a big believer in COALESCE() all of the time, but it turns out that ISNULL() is faster if you only have two things to compare. Granted, it’s not a huge difference in speed, as I recall, but the difference is there.

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Greg Low might have violated Betteridge’s Law of Headlines:

Using T-SQL it’s quite easy to build a table-valued function that can step through a string, character-by-character, and (based on a delimiter) output the delimited strings. The problem is that the performance of these functions is appalling.

When XML support appeared in SQL Server 2005, there were many attempts to create more efficient string-splitting functions. For many strings, these work quite well, but do have a few oddities that you need to cope with. Plus, most have limitations on the strings that you can split.

Ultimately, what was really needed was an efficient and native built-in function.  

Greg points out two mechanisms and contrasts them.

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Louis Davidson points out a neat update:

Sometimes along comes a feature that seems so obvious, so natural, that you wonder why it took so long for Microsoft to implement it. One of those features in SQL Server 2005 is the optional length parameter in the SUBSTRING function. It has long been one of those questions when you wrote a SUBSTRING expression when you wanted to go from the Nth character to the end of the string, how many characters do you want? And for the most part, it didn’t really matter.

But sometimes it did (especially when dealing with nvarchar(max) data.

I learned about this when putting together an update to my Teaching Old Dogs New Tricks presentation. This capability is pretty nifty and something I wish I had a while ago.

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Andy Brownsword can’t stop at one:

Having TOP (1) return multiple rows feels wrong… but that’s what WITH TIES can do.

For a long time I used patterns like this to get the first record in a group:

Andy goes on to explain how WITH TIES works in T-SQL, shows an alternative to using a common table expression + window function to narrow down to the first logical group, and digs into when you might not want to use that alternative.

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Louis Davidson runs some tests:

A month and a half ago, I wrote a blog on using DATE_BUCKET. It is a cool feature thta makes doing some grouping really quite easy. It is here: Cool features in SQL Server I missed…DATE_BUCKET. One of the comments that came in was about performance of the DATE_BUCKET versus using things like DATEDIFF or a date table.

I started working on it then, but it got a bit involved (as performance comparison tests often do), so it took me a bit longer to get to than expected. But here it is, and the results are kind of what you would expect. The uses for DATE_BUCKET are really straightforward, and would rarely involve an index or a lot of filtering using the the function. But over a large number of rows, if it takes more time (even a millisecond more) than another method, you would notice it pretty quickly adding up.

Read on to see how DATE_BUCKET() performs compared to other methods of solving the same problem.

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Jared Westover lays out some solid advice:

Imagine you’ve spent weeks preparing a software release for production, only to deploy it late one night and receive an error that the table or column already exists. This occurs in production environments, even when you use migration-based deployment methods such as DbUp. How can you ensure or at least reduce the likelihood of an error like this in the future?

At a prior job, we needed to write idempotent scripts because the deploy-to-QA process would run every script for the sprint every time someone checked in a new script. This prevented a few classes of release error, and I’ve carried that practice with me to future engagements.

SQL Server 2016 then gave us several helpers like CREATE OR ALTER for stored procedures and views, or DROP IF EXISTS for views and tables. It’s not a complete set of everything I’d like the functionality to do, but it’s a lot more convenient than what we had to do in prior versions.

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Greg Low shares some queries and some history:

Sequences allow us to create a schema-bound object that is not associated with any specific table.

For example, if I have a Sales.HotelBookings table, a Sales.FlightBookings table, and a Sales.VehicleBookings table, I might want to have a common BookingID used as the key for each table. If more than the BookingID was involved, you could argue that there is a normalization problem with the tables, but we’ll leave that discussion for another day.

Another reason I like sequences is that they make it much easier to override the auto-generated value, without the need for code like SET IDENTITY_INSERT that we need with IDENTITY columns. This is particularly powerful if you ever need to do this across linked servers, as you’ll quickly find out that it doesn’t work.

Sequences let me avoid these types of issues: they perform identically to IDENTITY columns, and they also give me more control over the cache for available values.

Click through for some queries to find the latest value of a sequence, as well as how this functionality has changed over the years. One thing that I would point out is that, on busy systems, you might find that the value has changed between the time you run this query and the time you use the results.

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