Does NULL have a data type?

Question

I ran into code similar to this today.

SELECT AuditDomain, 
    ObjectId,
    AuditSubdomain = CONVERT(VARCHAR(50), NULL),
    SubDomainObjectId = CONVERT(IN         


        

Answer 1

Null has no data type. The purpose of a null is to represent an "unknown", both in value and type.

ISNULL() returns the datatype for the first argument with a data type presented to it.

http://msdn.microsoft.com/en-us/library/ms187928.aspx