CONCAT_WS()

Manoj Pandey points out a new string function in SQL Server vNext:

Here in this post I’ll discuss about one more new function i.e. CONCAT_WS(), here “_WS” means “With Separator”.

This is very similar to the existing CONCAT() function introduced back in SQL Server 2012, which concatenates a variable number of arguments or string values.

The difference is the new function CONCAT_WS() accepts a delimiter specified as the 1st argument, and thus there is no need to repeat the delimiter after very String value like in CONCAT() function.

It’s a small change, but I think a rather useful one.  Do think about how you’d want to interpret NULL values, though, as CONCAT_WS() does not include separators for NULL values.

Multiple Operations Per Command

Louis Davidson points out a potential query writing time-saver:

But then I saw Mike use the following syntax (sans PROFILE and XML):

SET STATISTICS IO, TIME, PROFILE, XML ON;
GO
SELECT *
FROM   dbo.Table1;
GO
SET STATISTICS IO, TIME, PROFILE, XML OFF;

Wow, that is a lot easier! (And yeah, using SQL Prompt I can set a snippet to take away typing, but this saves space in any case.)

Read on for more examples.

Joins Galore

Lukas Eder has a comprehensive guide to joining data using SQL:

Alternative syntaxes: NATURAL JOIN

An more extreme and much less useful form of "EQUI" JOIN is the NATURAL JOIN clause. The previous example could be further “improved” by replacing USING by NATURAL JOIN like this:

SELECT *
FROM actor
NATURAL JOIN film_actor
NATURAL JOIN film

Notice how we no longer need to specify any JOIN criteria, because a NATURAL JOIN will automatically take all the columns that share the same name from both tables that it joins and place them in a “hidden” USING clause. As we’ve seen before, as primary keys and foreign keys have the same column name, this appears quite useful.

There is a high likelihood that you will learn at least one new thing here; for example, check out lateral joins (which SQL Server practitioners know as something else).

Wanted: Named Parameters For Functions

Riley Major would like to be able to specify parameter names in function calls:

Now try this:

DECLARE	@OrderID int = NULL,	@OrderType int = 1,	@Qty int = 2,	@ServiceSpeed int = 3;
SET @OrderID = dbo.GetOrderID (@OrderType, @Qty, @ServiceSpeed);
SELECT @OrderID 'Using SET Syntax';

Now you get a NULL back from the final SELECT. What happened? If you are a careful code reviewer, you might have spotted that the function definition has the @Qty and @ServiceSpeed parameters flipped as compared to the table definition and how we’re calling the function.

But this isn’t an error. There’s no obvious indication that anything is wrong. Imagine if instead of NULL, which would probably break something, you got a different order ID back. Your program would silently continue, oblivious to what is essentially data corruption.

And if you build a function with a large number of parameters, it gets that much easier accidentally to swap just two of them.  Click through for the rest of the story, and check out Riley’s Connect item.

Wanted: Automatic Columns

Louis Davidson plucks an old Connect item out for a new look:

The concept is very similar to a DEFAULT constraint, with two differences:

1. Will work on an UPDATE operation, without specifying DEFAULT

2. Could be configured to disallow the user from entering a value. My proposed syntax was pretty simple:

AUTO [WITH OVERRIDE] (scalar expression)

Now I realize that 10 years ago, I didn’t take terribly long to consider that WITH was a terrible thing to add to the syntax, and AUTO is a keyword already, so I am going to rename it: AUTO_DEFAULT (scalar expression, [option]). Since I have thought a bit more about this in the years since writing it, I realized there were a few more options that would be nice. I was terrible in college doing syntax parsing, but the syntax itself is not important. Temporal in SQL Server 2016 has syntax that is similar to this for the new temporal columns which I got really excited about the first time I saw it: SysStartTime datetime2 GENERATED ALWAYS AS ROW START NOT NULL. Maybe in vNext?

Read the whole thing.  Then check out the related Connect item Adam Machanic submitted.  I’d love to see that functionality, given how frequently I create these metadata columns.

Batches And Stored Procedure Creation

Steve Jones has a warning for when you create a stored procedure:

Why is my select code in there? That was designed to be a piece of test code. Shouldn’t the BEGIN..END after the AS define my procedure?

Actually it doesn’t. the procedure doesn’t end until the CREATE PROCEDURE statement is terminated. That termination comes by ending the batch. The CREATE PROCEDURE documentation has this limitation:

The CREATE PROCEDURE statement cannot be combined with other Transact-SQL statements in a single batch.

This means that anything else you have in that batch will be considered as part of the procedure, regardless of BEGIN..END.

Judicious usage of the GO statement can help keep you out of trouble.

STRING_AGG() Performance

Aaron Bertrand wants to know how the STRING_AGG() function performs:

We can see that our FORCESCAN hint really did make things worse – while we shifted the cost away from the clustered index seek, the sort was actually much worse, even though the estimated costs deemed them relatively equivalent. More importantly, we can see that STRING_AGG() does offer a performance benefit, whether or not the concatenated strings need to be ordered in a specific way. As with STRING_SPLIT(), which I looked at back in March, I am quite impressed that this function scales well prior to “v1.”

Given that the early releases tend to be “get the thing working” and later CTPs are around “make the thing faster,” it’s nice to see that STRING_AGG() is already ready for prime-time, and makes me wonder if they’ll make it even faster by RTM.

Pivoting Data

Jana Sattainathan explains the PIVOT operator:

The results are so much easier to look at and comprehend, aren’t they? All object types for a schema are on a single line and it is easy for us to do impact analysis visually.

Sometimes doing it in T-SQL is the best approach, but pivoting is generally something which is cheaper in the application tier, whether you’re building a report, dashboard, or web app.

SQL Order Of Operations

Kevin Feasel

2016-12-12

Syntax

Lukas Eder explains order of operations in a SQL query:

If you’re not a frequent SQL writer, the syntax can indeed be confusing. Especially GROUP BY and aggregations “infect” the rest of the entire SELECT clause, and things get really weird. When confronted with this weirdness, we have two options:

  • Get mad and scream at the SQL language designers
  • Accept our fate, close our eyes, forget about the snytax and remember the logicaloperations order

I generally recommend the latter, because then things start making a lot more sense, including the beautiful cumulative daily revenue calculation below, which nests the daily revenue (SUM(amount) aggregate function) inside of the cumulative revenue (SUM(...) OVER (...)window function):

Lukas explains things from an Oracle perspective, so not all of this matches T-SQL, but it’s close enough for comparison.

OUTPUT With Identity Columns

Kenneth Fisher walks through a scenario trying to archive data using the OUTPUT clause, but where there is an identity column involved:

So what’s the problem? Well, to start with by using the SELECT TOP 0 INTO Archive method of creating the Archive table you’ve created the archive table with an identity column. Get rid of that identity property (you still want the column) and you don’t have a problem. But the really cool part of this is that it reminded me that the OUTPUT clause has a field list.

Also check out the comments for another solution.

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