create FUNCTION dbo.f_hex_dec(@s varchar(max))  
RETURNS bigint  
AS  
BEGIN  
    DECLARE @i BIGINT ,  
        @result BIGINT 
         
    DECLARE @data BIGINT  --添加了这个
    SET @data =16
    
    SELECT  @i = 0 ,  
            @result = 0 ,  
            @s = RTRIM(LTRIM(UPPER(REVERSE(@s))))  
    WHILE @i < DATALENGTH(@s)   
        BEGIN  
            IF SUBSTRING(@s, @i + 1, 1) NOT BETWEEN '0' AND '9'  
                AND SUBSTRING(@s, @i + 1, 1) NOT BETWEEN 'A' AND 'F'   
                BEGIN  
                    SELECT  @result = 0  
                    BREAK  
                END  
            SELECT  @result = @result + ( CHARINDEX(SUBSTRING(@s, @i + 1, 1),  
                                                    '0123456789ABCDEF') - 1 )  
                    * POWER(@data, @i) ,  
                    @i = @i + 1  
        END  
    RETURN @result  
END  

SELECT dbo.f_hex_dec('7a7a003500bc0001')

--8825366647431495681