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DELIMITER $$
CREATE FUNCTION `mylength1`( s1 VARCHAR(255)) RETURNS int(11)
DETERMINISTIC
BEGIN
DECLARE s1_len, i INT;
SET s1_len = 0;
SET s1_len = s1_len+length(s1)+length(s1)+length(s1)+length(s1)+length(s1)+length(s1)+length(s1)+length(s1)+length(s1)+length(s1);
RETURN s1_len;
END;$$
DELIMITER $$
CREATE FUNCTION `mylength2`( s1 VARCHAR(255)) RETURNS int(11)
DETERMINISTIC
BEGIN
DECLARE s1_len, i INT;
SET s1_len = 0;
SET s1_len = s1_len+length(s1);
SET s1_len = s1_len+length(s1);
SET s1_len = s1_len+length(s1);
SET s1_len = s1_len+length(s1);
SET s1_len = s1_len+length(s1);
SET s1_len = s1_len+length(s1);
SET s1_len = s1_len+length(s1);
SET s1_len = s1_len+length(s1);
SET s1_len = s1_len+length(s1);
SET s1_len = s1_len+length(s1);
RETURN s1_len;
END;$$
DELIMITER $$
CREATE FUNCTION `mylength3`( s1 VARCHAR(255)) RETURNS int(11)
DETERMINISTIC
BEGIN
DECLARE s1_len, i INT;
SET s1_len = length(s1);
SET i = 0;
WHILE i <= 10 DO
SET s1_len = s1_len+length(s1);
SET i = i + 1;
END WHILE;
RETURN s1_len;
END;$$
select max(length(s)) a from tmp;
select max(length(s)+length(s)+length(s)+length(s)+length(s)+length(s)+length(s)+length(s)+length(s)+length(s)) a from tmp;
select max(mylength1(s)) from tmp a;
select max(mylength2(s)) from tmp a;
select max(mylength3(s)) from tmp a;
select max(levenshtein('任何一个字符串', s)) from tmp a;
升级版本就好了