.SQL Server中 image类型数据的比较

/****** Object:  UserDefinedFunction [dbo].[FuncCompareImage]    Script Date: 2016-09-01 11:18:53 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER FUNCTION [dbo].[FuncCompareImage] ( @a1 IMAGE, @a2 IMAGE )
RETURNS INT
-- if match, return 1
AS
    BEGIN
        DECLARE @n INT ,
            @i INT ,
            @j INT;
        DECLARE @b1 VARBINARY(8000) ,
            @b2 VARBINARY(8000);
        SET @n = 1;
        IF DATALENGTH(@a1) <> DATALENGTH(@a2) -- different length
            SET @n = 0;
        ELSE
            BEGIN
                SET @i = 0;
                SET @j = ( DATALENGTH(@a1) - 1 ) / 8000 + 1;
                WHILE @i <= @j
                    BEGIN
                        SET @b1 = SUBSTRING(@a1, @i * 8000 + 1,
                                            CASE @i
                                              WHEN @j
                                              THEN DATALENGTH(@a1) % 8000
                                              ELSE 8000
                                            END);
                        SET @b2 = SUBSTRING(@a2, @i * 8000 + 1,
                                            CASE @i
                                              WHEN @j
                                              THEN DATALENGTH(@a2) % 8000
                                              ELSE 8000
                                            END);
                        IF @b1 <> @b2
                            BEGIN
                                SET @n = 0;
                                BREAK;
                            END;
                        SET @i = @i + 1;
                    END;
            END;
        RETURN(@n);
    END;