MySQL Stored Procedure to Loop Delimited List

mysql_list_loop.sql

DELIMITER $$
DROP PROCEDURE IF EXISTS LOOP_STUFF$$
CREATE PROCEDURE LOOP_STUFF(IN STR_TXT VARCHAR(255))
    BEGIN
	/* DECLARE VARIABLES FOR USE IN LOOP */
	DECLARE STR_LEN  INT DEFAULT 0;
	DECLARE SUB_LEN  INT DEFAULT 0;	
	DECLARE SUB_TXT  VARCHAR(255);
	DECLARE COUNTER  INT DEFAULT 0;
	
	/* STORES FINAL RESULT */
	SET @RESULT = '';
	
	/* HANDLE NULL ARGUMENT ERROR */
	IF STR_TXT IS NULL THEN SET STR_TXT = ''; END IF;
	
	DO_LOOP:
	    LOOP
		/* GET LENGTH OF FULL REMAINING STRING TO GET ELEMENT POSITION */
		SET STR_LEN = CHAR_LENGTH(STR_TXT);

		/* USE LENGTH OF THIS ELEMENT'S SUBSTRING FOR ELEMENT EXTRACTION */
		SET SUB_LEN = CHAR_LENGTH(SUBSTRING_INDEX(STR_TXT, ',', 1)) + 2;

		/* EXTRACT LIST ELEMENT CORRESPONDING TO THIS ITERATION) */
		/* REPLACE COMMA WITH DELIMITER OF YOUR CHOICE IF NECESSARY */
		SET SUB_TXT = REPLACE(REPLACE(STR_TXT, MID(STR_TXT, SUB_LEN, STR_LEN), ''), ',', '');

		/* REMOVE ELEMENT FROM LIST */
		SET STR_TXT = MID(STR_TXT, SUB_LEN, STR_LEN);
		
		/* DETERMINE WHETHER ELEMENT IS FIRST IN LIST */
		/* NOW YOU CAN USE CONDITIONAL LOGIC TO CONCAT TOGETHER A SQL STRING 
		   TO @RESULT AND EXECUTE IT WITH PREPARE/EXECUTE/DEALLOCATE PREPARED STATEMENT */
		IF COUNTER = 0 THEN
			/* DO STUFF WITH FIRST ITERATION OF LOOP HERE */
			SET @RESULT = CONCAT(@RESULT, SUB_TXT);
		ELSE
			/* DO STUFF WITH OTHER ITERATIONS E.G. CHANGE DELIMITER TO PIPELINE */
			SET @RESULT = CONCAT(@RESULT, '|', SUB_TXT);
		END IF;
		
		/* INCREMENT COUNTER */
		SET COUNTER = COUNTER + 1;

		/* EXIT LOOP WHEN STRING EMPTY */
		IF STR_TXT = '' THEN LEAVE DO_LOOP; END IF;
	    END LOOP 
	DO_LOOP;

	/* OUTPUT RESULT */
	SELECT @RESULT;
    END$$
DELIMITER ;
CALL LOOP_STUFF('A,B,C');