conditional stored procedure with/without passing parameter

Question

I created a stored procedure which when passed nothing as parameter should return the entire table. But if the studentId is passed, then return her details. Something like t

Answer 1

You're trying to test for null using =, a comparison operator. If you're using ANSI nulls, any comparison against null is false.

Where @studentId is any value (or null) the following expressions are all false:

@studentId = null  -- false
@studentId > null  -- false
@studentId >= null  -- false
@studentId < null  -- false
@studentId <= null  -- false
@studentId <> null -- false

So, in order to test for null you must use a special predicate, is null, i.e.:

@studentId is null