Oracle 的INSTR函数MySQL实现

一个迁移项目遇到的，MySQL的instr函数只能查找子串是否在父串中，没法按照出现的次数进行查找。 
这里我自己写了一个，以便迁移。当然我这里仅仅针对的是迁移，可能没有完全实现原有函数的细节。


Oracle 里用了几次如下的调用，

SQL> select instr('This is belong to you, but not to me.','to',1,1) as pos from dual;

POS
--------------------
16

已用时间:  00: 00: 00.00
SQL> select instr('This is belong to you, but not to me.','to',1,2) as pos from dual;

POS
--------------------
32

已用时间:  00: 00: 00.00
SQL> select instr('This is belong to you, but not to me.','belong',-1,1) as pos from dual;

POS
--------------------
9

已用时间:  00: 00: 00.00
SQL> select instr('This is belong to you, but not to me.','belong',-1,2) as pos from dual;

POS
--------------------
0

已用时间:  00: 00: 00.00

MySQL里效果如下，

mysql> select func_instr_oracle('This is belong to you, but not to me.','to',1,1) as pos;
+------+
| pos  |
+------+
|   16 |
+------+
1 row in set (0.00 sec)

mysql> select func_instr_oracle('This is belong to you, but not to me.','to',1,2) as pos;
+------+
| pos  |
+------+
|   32 |
+------+
1 row in set (0.00 sec)

mysql> select func_instr_oracle('This is belong to you, but not to me.','belong',-1,1) as pos;
+------+
| pos  |
+------+
|    9 |
+------+
1 row in set (0.00 sec)

mysql> select func_instr_oracle('This is belong to you, but not to me.','belong',-1,2) as pos;
+------+
| pos  |
+------+
|    0 |
+------+
1 row in set (0.00 sec)

附上函数func_instr_oracle的代码：

DELIMITER $$

USE `oracle12c`$$

DROP FUNCTION IF EXISTS `func_instr_oracle`$$

CREATE DEFINER=`root`@`localhost` FUNCTION `func_instr_oracle`(
f_str VARCHAR(1000), -- Parameter 1
f_substr VARCHAR(100), -- Parameter 2
f_str_pos INT, -- Postion
f_count INT UNSIGNED -- Times
) RETURNS INT(10) UNSIGNED
BEGIN
-- Created by ytt. Simulating Oracle instr function.
-- Date 2015/12/5.
DECLARE i INT DEFAULT 0; -- Postion iterator
DECLARE j INT DEFAULT 0; -- Times compare.
DECLARE v_substr_len INT UNSIGNED DEFAULT 0; -- Length for Parameter 1.
DECLARE v_str_len INT UNSIGNED DEFAULT 0; -- Length for Parameter 2.
SET v_str_len = LENGTH(f_str);
SET v_substr_len = LENGTH(f_substr);
-- Unsigned.
IF f_str_pos > 0 THEN
SET i = f_str_pos;
SET j = 0;
WHILE i <= v_str_len
DO
IF INSTR(LEFT(SUBSTR(f_str,i),v_substr_len),f_substr) > 0 THEN
SET j = j + 1;
IF j = f_count THEN
RETURN i;
END IF;
END IF;
SET i = i + 1;
END WHILE;
-- Signed.
ELSEIF f_str_pos <0 THEN
SET i = v_str_len + f_str_pos+1;
SET j = 0;
WHILE i <= v_str_len AND i > 0
DO
IF INSTR(RIGHT(SUBSTR(f_str,1,i),v_substr_len),f_substr) > 0 THEN
SET j = j + 1;
IF j = f_count THEN
RETURN i - v_substr_len + 1;
END IF;
END IF;
SET i = i - 1;
END WHILE;
-- Equal to 0.
ELSE
RETURN 0;
END IF;
RETURN 0;
END$$

DELIMITER ;