How do you specify 'DEFAULT' as a SQL parameter value in ADO.NET?

Question

I have a parameterized SQL query targetted for SQL2005 which is dynamically created in code, so I used the ADO.NET SqlParameter class to add sql parameters to SqlCommand.

In the aforementioned SQL I select from a Table Valued Function with has defaults. I want my dynamic sql to sometimes specify a value for these default parameters, and other times I want to specify that the SQL DEFAULT - as defined in the Table Valued Function - should be used.

To keep the code clean I didn't want to dynamically add the SQL DEFAULT keyword and parameterize it when a non-default is to be used, I just wanted to set DEFAULT as the value of my SQLParameter.

Can I? What is best practice in such an instance?

Answer 1

AFAIK, the only way to tell SQL Server to use a default value is via the DEFAULT keyword or to exclude it from parameter list. That means that the use of the DEFAULT keyword must be in your parameterized SQL Statement. So, something like:

Select ...
From dbo.udf_Foo( DEFAULT, @Param2, @Param3, DEFAULT, .... )

I suppose another approach would be to query the system catalogs for the actual value of the various DEFAULT values and determine whether to set the SqlParameter to the default value that way, but that requires a convoluted second query to get the default values.

Answer 2

SQL query parameters take the place of literal values only.

You can't send an SQL keyword as the value of a parameter, just as you cannot send a table identifier, column identifier, list of values (e.g. for an IN predicate), or an expression. The value of the parameter is always interpreted as a literal value, as if you had included a quoted string literal or a numeric literal in your query.

Sorry, but you have to include an SQL keyword as part of the SQL query before you prepare that query.