mysql随机数

DELIMITER $$
CREATE DEFINER = `root` @`localhost` FUNCTION `func_range_string_mod` ( f_num INT UNSIGNED -- Total strings.
) RETURNS VARCHAR ( 200 ) CHARSET latin1 BEGIN
DECLARE
    i INT UNSIGNED DEFAULT 0;
DECLARE
    v_result VARCHAR ( 200 ) DEFAULT '';
DECLARE
    v_dict VARCHAR ( 200 ) DEFAULT '';

SET v_dict = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';

SET v_dict = LPAD( v_dict, 200, v_dict );
WHILE
        i < f_num DO
        
        SET v_result = CONCAT( v_result, SUBSTR( v_dict, CEIL( RAND( ) * 200 ), 1 ) );
    
    SET i = i + 1;
    
END WHILE;
RETURN v_result;

END $$DELIMITER;

SELECT func_range_string_mod(6);