mysql 字符串去头去尾 mysql字符串提取数字

DELIMITER $$
DROP FUNCTION IF EXISTS `Num_char_extract`$$
CREATE FUNCTION `Num_char_extract`(Varstring VARCHAR(100)CHARSET utf8, flag INT) RETURNS VARCHAR(50) CHARSET utf8
COMMENT '标识 0 提取数字 1 提取字母 2提取数字+字母 3 提取汉字 4 提取汉字+数字+字母'
BEGIN
    DECLARE len INT DEFAULT 0;
    DECLARE Tmp VARCHAR(100) DEFAULT '';
    SET len=CHAR_LENGTH(Varstring);
    IF flag = 0
    THEN
        WHILE len > 0 DO
        IF MID(Varstring,len,1)REGEXP'[0-9]' THEN
        SET Tmp=CONCAT(Tmp,MID(Varstring,len,1));
        END IF;
        SET len = len - 1;
        END WHILE;
    ELSEIF flag=1
    THEN
        WHILE len > 0 DO
        IF (MID(Varstring,len,1)REGEXP '[a-zA-Z]')
        THEN
        SET Tmp=CONCAT(Tmp,MID(Varstring,len,1));
        END IF;
        SET len = len - 1;
        END WHILE;
    ELSEIF flag=2
    THEN
        WHILE len > 0 DO
        IF ( (MID(Varstring,len,1)REGEXP'[0-9]')
        OR (MID(Varstring,len,1)REGEXP '[a-zA-Z]') )
        THEN
        SET Tmp=CONCAT(Tmp,MID(Varstring,len,1));
        END IF;
        SET len = len - 1;
        END WHILE;
    ELSEIF flag=3
    THEN
        WHILE len > 0 DO
        IF NOT (MID(Varstring,len,1)REGEXP '^[u0391-uFFE5]')
        THEN
        SET Tmp=CONCAT(Tmp,MID(Varstring,len,1));
        END IF;
        SET len = len - 1;
        END WHILE;
    ELSEIF flag=4
    THEN
        WHILE len > 0 DO
        IF ( (MID(Varstring,len,1)REGEXP'[0-9]')
        OR (MID(Varstring,len,1)REGEXP '[a-zA-Z]')
        OR ((HEX(MID(Varstring,len,1)) REGEXP '^(..)*(E[4-9])' ))
        )
        THEN
        SET Tmp=CONCAT(Tmp,MID(Varstring,len,1));
        END IF;
        SET len = len - 1;
        END WHILE;
    ELSE
        SET Tmp = 'Error: The second paramter should be in (0,1,2,3,4)';
        RETURN Tmp;
    END IF;
    RETURN REVERSE(Tmp);
    END$$
DELIMITER ;

检验：

SELECT Num_char_extract('哈112asdd****&，...，',1);

SELECT Num_char_extract('哈112asdd****&，...，',2);

SELECT Num_char_extract('哈112asdd****&，...，',3);

SELECT Num_char_extract('哈112asdd****&，...，',4);