length:返回字符串所占的字节数，是计算字段的长度。utf8编码下,一个汉字是算三个字符,一个数字或字母算一个字符。其他编码下,一个汉字算两个字符, 一个数字或字母算一个字符。 
char_length:返回字符串所占的字符数，不管汉字还是数字或者是字母都算是一个字符

DELIMITER $$
CREATE DEFINER=`testuser`@`%` PROCEDURE `getMaxSubStrP`(`inParam1` varchar(100),`inParam2` varchar(100), out `resultStr` VARCHAR(100), out `resultLen` int)
BEGIN
   DECLARE longStr VARCHAR(255);
   DECLARE shortStr VARCHAR(255);
   DECLARE tempStr VARCHAR(255);
   DECLARE tempResult VARCHAR(255) DEFAULT "";
   DECLARE strLength1 INT DEFAULT 0;
   DECLARE strLength2 INT DEFAULT 0;
   DECLARE minStrLength INT DEFAULT 0;
   DECLARE startIndex INT DEFAULT 0;
   DECLARE endIndex INT DEFAULT 1;
   DECLARE cmpInt   INT DEFAULT 0;
    
   SELECT CHAR_LENGTH(inParam1), CHAR_LENGTH(inParam2) INTO strLength1,strLength2 FROM DUAL;
  
   SET minStrLength = strLength1;
 
   IF  minStrLength>strLength2 THEN
       SET minStrLength=strLength2;
       SET longStr =  inParam1;
       SET shortStr = inParam2;
   ELSE
       SET longStr=inParam2;
       SET shortStr=inParam1;
   end if;


   -- select minStrLength,longStr,shortStr;
   
    WHILE startIndex < minStrLength
    DO
        SET endIndex = startIndex + 1;
        WHILE endIndex<=minStrLength
        DO
              SELECT SUBSTR(shortStr,startIndex+1,endIndex-startIndex) into tempStr from DUAL;
              SELECT INSTR(longStr, tempStr ) into cmpInt FROM dual;
          -- select startIndex,endIndex,tempStr,tempResult,cmpInt;
             IF (cmpInt>0) AND (CHAR_LENGTH(tempResult)<char_length(tempstr)) then  THEN            
              SET tempResult=tempStr;
             END if;
             SET endIndex = endIndex + 1;
       end WHILE; -- endIndex while
       set startIndex = startIndex + 1;
    end while; -- startIndex WHILE
   
   set resultStr=tempResult;
   SELECT CHAR_LENGTH(resultStr) INTO resultLen FROM DUAL;
   -- set resultLen= CHAR_LENGTH(resultStr);
   -- select @resultLen,@resultStr;

END$$
DELIMITER ;