Category: T-SQL

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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