27 May 2011

Some Original Expressions

Guest Editorial for Simple-Talk newsletter

In a guest editorial for the Simple-Talk Newsletter, Phil Factor wonders if we are still likely to find some more novel and unexpected ways of using the newer features of Transact SQL: or maybe in some features that have always been there!

There can be a great deal of fun to be had in trying out recent features of SQL Expressions to see if  they provide new functionality.  It is surprisingly rare to find things that couldn’t be done before, but in a different   and more cumbersome way; but it is great to experiment or to read of someone else making that discovery.  One such recent feature is the ‘table value constructor, or ‘VALUES constructor’, that managed to get into SQL Server 2008 from Standard SQL.  This allows you to create derived tables of up to 1000 rows neatly within select statements that consist of  lists of row values.  E.g.

SELECT Old_Welsh, number FROM (VALUES (‘Un’,1),(‘Dou’,2),(‘Tri’,3),(‘Petuar’,4),(‘Pimp’,5),(‘Chwech’,6),(‘Seith’,7),(‘Wyth’,8),(‘Nau’,9),(‘Dec’,10)) AS WelshWordsToTen (Old_Welsh, number)

These values can be expressions that return single values, including, surprisingly, subqueries. You can use this device to create views, or in the USING clause of a MERGE statement. Joe Celko covered  this here and here.  It can become extraordinarily handy to use once one gets into the way of thinking in these terms, and I’ve rewritten a lot of routines to use the constructor, but the old way of using UNION can be used the same way, but is a little slower and more long-winded.

The use of scalar SQL subqueries as an expression in a VALUES constructor, and then applied to a MERGE, has got me thinking. It looks very clever, but what use could one put it to? I haven’t seen anything yet that couldn’t be done almost as  simply in SQL Server 2000, but I’m hopeful that someone will come up with a way of solving a tricky problem, just in the same way that a freak of the XML syntax forever made the in-line  production of delimited lists from an expression easy, or that a weird XML pirouette could do an elegant  pivot-table rotation.

It is in this sort of experimentation where the community of users can make a real contribution. The dissemination of techniques such as the Number, or Tally table, or the unconventional ways that the UPDATE statement can be used, has been rapid due to articles and blogs. However, there is plenty to be done to explore some of the less obvious features of Transact SQL. Even some of the features introduced into SQL Server 2000 are hardly well-known.

Certain operations on data are still awkward to perform in Transact SQL, but we mustn’t, I think, be too ready to state that certain things can only be done in the application layer, or using a CLR routine. With the vast array of features in the product, and with the tools that surround it, I feel that there is generally a way of getting tricky things done. Or should we just stick to our lasts and push anything difficult out into procedural code? I’d love to know your views.

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Phil Factor (real name withheld to protect the guilty), aka Database Mole, has 30 years of experience with database-intensive applications. Despite having once been shouted at by a furious Bill Gates at an exhibition in the early 1980s, he has remained resolutely anonymous throughout his career. See also :

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