Oracle 的INSTR函數MySQL實作

一個遷移項目遇到的，MySQL的instr函數隻能查找子串是否在父串中，沒法按照出現的次數進行查找。 

這裡我自己寫了一個，以便遷移。當然我這裡僅僅針對的是遷移，可能沒有完全實作原有函數的細節。

Oracle 裡用了幾次如下的調用，

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


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


已用時間:  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                              


已用時間:  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                              


已用時間:  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                              


已用時間:  00: 00: 00.00
           

MySQL裡效果如下，

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)
           

附上函數func_instr_oracle的代碼：

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 ;