Replaces NULL with the specified replacement value.
ISNULL ( check_expression , replacement_value )
Is the expression to be checked for NULL. check_expression can be of any type.
Is the expression to be returned if check_expression is NULL. replacement_value must be of a type that is implicitly convertible to the type of check_expression.
Returns the same type as check_expression. If a literal NULL is provided as check_expression, returns the datatype of the replacement_value. If a literal NULL is provided as check_expression and no replacement_value is provided, returns an int.
SELECT ISNULL('abc', 2.5) as X;