mysql字段中提取汉字，去除数字以及字母

如果只是删除尾部的中文，保留数据，可以用以下的简单方式

MySQL [test]> select '1234万美元' + 0 as num;
+------+
| num  |
+------+
| 1234 |
+------+

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'
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;
    ELSE
        SET Tmp = 'Error: The second paramter should be in (0,1,2,3)';
        RETURN Tmp;
    END IF;
    RETURN REVERSE(Tmp);
    END$$
DELIMITER ;

-- select Num_char_extract('字12段',0);