SET ANSI_NULLS ON;
DECLARE @1 INT;
DECLARE @2 INT;
DECLARE @3 INT;
DECLARE @4 INT;

SET @1 = 1;
SET @2 = NULL;
SET @3 = 3;
SET @4 = 3;

IF ((@1 <> @2) OR (@3 <> @4))
   BEGIN
     SELECT 1;
   END
ELSE
   BEGIN
     SELECT 2;
   END
SELECT @1, @2, @3, @4

2

1, NULL, 3, 3

1

1, NULL, 3, 3

IF ((ISNULL(@1, -1) <> ISNULL(@2, -1)) OR (ISNULL(@3, -1) <> ISNULL(@4, -1)))
   BEGIN
     SELECT 1;
   END
ELSE
   BEGIN
     SELECT 2;
   END

IF ((@1 <> @2)
OR (@1 is NULL AND @1 IS NOT NULL)
OR (@1 is NOT NULL AND @1 IS NULL)
OR (@3 <> @4)
OR (@3 is NULL AND @4 IS NOT NULL)
OR (@3 is NOT NULL AND @4 IS NULL))

IF ((IsNull(@1,-1) <> IsNull(@2,-1)
OR (IsNull(@3,-1) <> IsNull(@4,-1))

SET @1 = IsNull(@1,-1);

IF (@1 IS NULL AND @2 IS NULL) OR (@1 = @2)
BEGIN
    IF (@3 IS NULL AND @4 IS NULL) OR (@3 = @4)
    BEGIN
        SELECT 2
    END
    ELSE
    BEGIN
        SELECT 1
    END
END
ELSE
BEGIN
    SELECT 1
END

SET ANSI_NULLS ON;
DECLARE @1 INT;
DECLARE @2 INT;
DECLARE @3 INT;
DECLARE @4 INT;
SET @1 = 1;
SET @2 = NULL;
SET @3 = 3;
SET @4 = 3;
IF ((@1 = @2) AND (@3 = @4))
   BEGIN     SELECT 1;
   ENDELSE
   BEGIN     SELECT 2;
   END
SELECT @1, @2, @3, @4