Adding an Else to your Switch

In this short article I will be talking about two functions in the SQL Server Reporting Services (SSRS) function stack.  Those functions are IIF() and Switch().  And I'll be showing you how easy it is to add an Else part to the Switch function.

Two commonly-used functions in SQL Server Reporting Services are the IIF() and the Switch().  These are two functions of the Program Flow type, or Decision Functions as they are called on this MSDN page.

In case you're wondering why it's so difficult to find a function reference for the built-in functions of SSRS, it's because these are actually Visual Basic functions and Microsoft refers to those for any detailed explanation.  Their references are located at the bottom of this article.

Anyone who's done some programming most likely already knows the if <expression> then <some_code> else <other_code> statement.  If <expression> evaluates to true then <some_code> gets executed, else <other_code>  gets executed.

The IIF() works in the same way.  According to its description it:

Returns one of two objects, depending on the evaluation of an expression.

This is its definition:

Public Function IIf( _
                          ByVal Expression As Boolean, _
                          ByVal TruePart As Object, _
                          ByVal FalsePart As Object _
                      ) As Object
                      

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Here's a simple example.

=IIf(Fields!YearlyIncome.Value >= 600,"High","Low")
                      

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Using this expression, the "High" string is returned when the value of the YearlyIncome field is equal to or above 600, while the string "Low" is returned when the value is below 600.

Now have a look at the following example.  It has been nicely structured with indentation and line breaks to make reading easier.

=IIF
                      (
                          Sum(Fields!LineTotal.Value) >= 100,
                          "Violet",
                          IIF
                          (
                              Sum(Fields!LineTotal.Value) < 25,
                              "Transparent",
                              "Cornsilk"
                          )
                      )
                      

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As you see, it shows a nested IIF inside another one.  Imagine that there were several more nestings and that line breaks were not used by the coder.  Would be a nightmare to read, right?

That's why the Switch() was invented.  The description for the Switch function reads:

Evaluates a list of expressions and returns an Object value corresponding to the first expression in the list that is True.

And this is the function definition:

Public Function Switch( _
                          ByVal ParamArray VarExpr() As Object _
                      ) As Object
                      

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In Reporting Services, the VarExpr parameter is simply an even list of expressions and/or object references separated by commas.  Which comes down to something like this: Switch(<expr1>, val1, <expr2>, val2).

Here's a simple example:

=Switch
                      (
                      	Fields!State.Value = "OR", "Oregon",
                      	Fields!State.Value = "WA", "Washington"
                      )
                      

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This expression says that if the value for the State field is "OR" then the Switch function will return "Oregon", and so on...

Now, to get to the point of this article, the Switch function does not contain an ELSE part like the IIF does.

But I wouldn't be writing this if there wasn't a workaround, would I?  If you read the Switch's description closely, it says that it will return the first expression in the list that is true.  So each expression is evaluated in the order that they are passed to the function.  To get ELSE-like behavior we would need an expression that evaluates to True but only when all other expressions are False.  So, why not use True as expression?  It's the simplest expression that I can think of and it does the works!

Have a look at the following, it's a rewrite of the last IIF example mentioned earlier.

=Switch
                      (
                          Sum(Fields!LineTotal.Value) >= 100, "Violet",
                          Sum(Fields!LineTotal.Value) < 25, "Transparent",
                          True, "Cornsilk"
                      )
                      

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So, which one do you think is the most readable?  The IIF, or the Switch?  These are only simple examples that I've been using, imagine situations with ten or more possibilities.  Well, I think you've got my point by now.

Thank you for reading this article, and remember: Happy Reporting!  Don't forget the little YES button on the way out ;-)

Valentino.

Originally appeared on my website: http://blog.hoegaerden.be/2009/09/14/adding-an-else-to-your-switch 

References
MSDN VS2008 VB.NET IIf Function
MSDN VS2008 VB.NET Switch Function