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

From the above, short circuiting is not really available.

If you need it, I suggest a Case statement:

Where Case when Expr1 then Expr2 else Expr3 end = desiredResult

Expr1is always evaluated, but only one of Expr2 and Expr3 will be evaluated per row.