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Category: Syntax

Batches And Stored Procedure Creation

Published 2017-01-04 by Kevin Feasel

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.

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STRING_AGG() Performance

Published 2016-12-29 by Kevin Feasel

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.

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Pivoting Data

Published 2016-12-22 by Kevin Feasel

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.

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SQL Order Of Operations

Published 2016-12-12 by Kevin Feasel

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.

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OUTPUT With Identity Columns

Published 2016-12-01 by Kevin Feasel

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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Brackets Don’t Improve Performance

Published 2016-11-11 by Kevin Feasel

Jay Robinson shows that wrapping identifiers with brackets does nothing for performance:

Anyway, this obsession had me thinking – does wrapping identifiers in square brackets save SQL Server any time? Does it say to the optimizer, “Hey, I PROMISE this whole thing inside these square brackets is an identifier. Cross my heart.” And the optimizer takes your code at its word and doesn’t look through its list of reserved keywords for one that matches AccountCreateDate or address_line_2?

The answer is… no. Throwing every identifier into square brackets doesn’t speed it up at all. Here’s the test:

Read on for the test.

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Concatenation Using CONCAT

Published 2016-11-07 by Kevin Feasel

Neil Gelder has a look at the CONCAT() function in SQL Server 2012:

This function removes all need to convert values just to concatenate text and string values together, but for some reason whenever I see code posted on various websites, even from SQL Server MVP’s they seem never to utilise this function.

One excellent use for this is when you attempting to created the SQL Statement for a dynamic SQL execution.  Instead of the usual conversions and + signs joining the text and parameters together its far simpler.

CONCAT is one of my favorite T-SQL enhancements from 2012 (after window functions).

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Cast Or Convert

Published 2016-11-03 by Kevin Feasel

Aaron Bertrand discusses the Cast and Convert functions:

Neither is really any more typing than the other, and they both work the exact same way under the covers. So it would seem that the choice between CASTand CONVERT is merely a subjective style preference. If that were always true, however, you probably wouldn’t be reading this post.

There are other cases where you need to use CONVERT in order to output correct data or perform the right comparison. Some examples:

Read on for examples.  My preference is CAST, mostly because it’s fewer characters to type.  But there are certainly advantages to using CONVERT.

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Logical Windowing

Published 2016-11-03 by Kevin Feasel

Lukas Eder discusses window functions:

Now, let’s assume I’m interested in these things:

  1. How many payments were there in the same hour as any given payment?
  2. How many payments were there in the same hour before any given payment?
  3. How many payments were there within one hour before any given payment?

Those are three entirely different questions.

Lukas’s solution uses Oracle syntax, but most of it also applies to SQL Server 2012 and higher.  The part that doesn’t apply, unfortunately, is the RANGE BETWEEN INTERVAL, which allows you to find values clustered in the same time period (one hour in his example).

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ISNULL And COALESCE Behavior Difference

Published 2016-10-10 by Kevin Feasel

Vladimir Oselsky notes an edge case where ISNULL and COALESCE can behave differently:

Even though we would expect to see both records returned we only get 1 record. Huh? This is exactly what puzzled a coworker, ofcourse query was not as simple as this one but same issue caused him to hit a road block.

In the case of COALESCE and OR methods, results are identical.

The underlying issue here is that the variable data type differs from the column’s data type, and exposes a difference in how COALESCE and ISNULL work.

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