Nakul,

Nice article. One small problem I noticed was that the constraint for being 18 years old was given as:

(DATEDIFF(YEAR,BirthDate,GETDATE()) >= 18);

That won't give the correct answer when the birthdate is later in the year than the current date. Wouldn't it be better to use:

(DATEADD(YEAR, -18,GETDATE()) >= BirthDate);