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DELIMITER // -- 修改MySQL delimiter：'//'
DROP FUNCTION IF EXISTS `rand_string` //
CREATE FUNCTION `rand_string` (n INT) RETURNS VARCHAR(255) CHARSET 'utf8'
BEGIN
DECLARE char_str varchar(100) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
DECLARE return_str varchar(255) DEFAULT '';
DECLARE i INT DEFAULT 0;
WHILE i < n DO
SET return_str = concat(return_str, substring(char_str, FLOOR(1 + RAND()*62), 1));
SET i = i+1;
END WHILE;
RETURN return_str;
END //
DELIMITER ;