原文：https://blog.csdn.net/oyezhou/article/details/81665643
另外一篇類似的：https://blog.csdn.net/haijiege/article/details/79460236

建立一個Num_char_extract.sql檔案,內容如下，在mysql shell中使用source執行，這樣就新建了一個函式。

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
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 ;

mysql> source /tmp/tmpcode/Num_char_extract.sql
Query OK, 0 rows affected, 1 warning (0.00 sec)

Query OK, 0 rows affected (0.15 sec)

測試效果

mysql> select Num_char_extract("123中國ABC",0);
+------------------------------------+
| Num_char_extract("123中國ABC",0)   |
+------------------------------------+
| 123                                |
+------------------------------------+
1 row in set (0.06 sec)

mysql> select Num_char_extract("123中國ABC",2);
+------------------------------------+
| Num_char_extract("123中國ABC",2)   |
+------------------------------------+
| 123ABC                             |
+------------------------------------+
1 row in set (0.00 sec)

mysql> select Num_char_extract("123中國ABC",3);
+------------------------------------+
| Num_char_extract("123中國ABC",3)   |
+------------------------------------+
| 中國                               |
+------------------------------------+
1 row in set (0.00 sec)

mysql> insert into t2(name) values("1500萬人民幣元"),("300美元"),("54648萬人民幣"),("855598萬日元");
Query OK, 4 rows affected (0.14 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> select name from t2;
+---------------------+
| name                |
+---------------------+
| 1500萬人民幣元      |
| 300美元             |
| 54648萬人民幣       |
| 855598萬日元        |
+---------------------+
4 rows in set (0.00 sec)

mysql> select name,Num_char_extract(name,3) from t2;
+---------------------+--------------------------+
| name                | Num_char_extract(name,3) |
+---------------------+--------------------------+
| 1500萬人民幣元      | 萬人民幣元               |
| 300美元             | 美元                     |
| 54648萬人民幣       | 萬人民幣                 |
| 855598萬日元        | 萬日元                   |
+---------------------+--------------------------+
4 rows in set (0.00 sec)