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 don't know about short circuting, but i'd write it as an if-else statement

if (@key is null)
begin

     SELECT * 
     FROM Table t 

end
else
begin

     SELECT * 
     FROM Table t 
     WHERE t.Key=@key

end

also, variables should always be on the right side of the equation. this makes it sargable.

http://en.wikipedia.org/wiki/Sargable