【原创】oracle函数INSTR的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 ;