Is the SQL WHERE clause short-circuit evaluated?

Question

Are boolean expressions in SQL WHERE clauses short-circuit evaluated ?

For example:

SELECT * 
FROM Table t 
WHERE @key IS NULL OR (@key IS NOT NULL          


        

Answer 1

I typically use this for optional parameters. Is this the same as short circuiting?

SELECT  [blah]
FROM    Emp
WHERE  ((@EmpID = -1) OR (@EmpID = EmpID))

This gives me the option to pass in -1 or whatever to account for optional checking of an attribute. Sometimes this involves joining on multiple tables, or preferably a view.

Very handy, not entirely sure of the extra work that it gives to the db engine.