How to realize the function of oracle function INSTR by MySQL

Let me tell you a little bit about how MySQL implements the function of oracle function INSTR. Have you ever heard of similar topics before? If you are interested, let's take a look at this article. I believe it will be more or less helpful for everyone to read how MySQL implements the function INSTR of oracle.

The following calls are used several times in Oracle

SQL > select instr ('This is belong to you, but not to me.','to',1,1) as pos from dual POS-16 elapsed time: 00: 00: 00.00SQL > select instr ('This is belong to you, but not to me.','to',1,2) as pos from dual POS-32 elapsed time: 00: 00: 00.00SQL > select instr ('This is belong to you, but not to me.','belong',-1,1) as pos from dual POS-9 elapsed time: 00: 00: 00.00SQL > select instr ('This is belong to you, but not to me.','belong',-1,2) as pos from dual POS-0 elapsed time: 00: 00: 00.00

The effect in MySQL is as follows

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)

Attach the code for the function func_instr_oracle:

DELIMITER $$USE `oracle12c` $DROP FUNCTION IF EXISTS `oracle` $$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) UNSIGNEDBEGIN-- 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 = fancistrampoup; SET j = 0; WHILE I 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 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

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