A UDF to split strings based on a delimiter in MySQL

split_string.sql

-- Select your database
USE sample_database;
/* You might need to run this if MySQL says that the below function is non-determininstic (although I've added DETERMINSTIC keyword in it) */
-- SET GLOBAL log_bin_trust_function_creators = 1;
DELIMITER $$
DROP FUNCTION IF EXISTS splitString $$
-- Function splitString that returns a substring based on a certain delimiter's position
CREATE FUNCTION splitString (        
        x VARCHAR(255),
        delim VARCHAR(12),
        pos INT
        )
        RETURNS VARCHAR(255) DETERMINISTIC
        RETURN REPLACE(SUBSTRING(SUBSTRING_INDEX(x, delim, pos),
         LENGTH(SUBSTRING_INDEX(x, delim, pos -1)) + 1),
         delim, '') $$
DROP PROCEDURE IF EXISTS getAllStrings $$
-- Procedure to get all the words from the input string passed to it as argument
CREATE PROCEDURE getAllStrings(IN idString varchar(256)) 
    BEGIN
		CREATE TEMPORARY TABLE IF NOT EXISTS tbl_temp_sep_strings( SPLIT_VALUES VARCHAR(256));
		SELECT LENGTH(idString) - LENGTH(REPLACE(idString, ', ', '')) INTO @noOfCommas;
			   IF  @noOfCommas = 0 
			  THEN
					INSERT INTO tbl_temp_sep_strings(SPLIT_VALUES) values(idString);
			  ELSE 
                    SET @y = 1;
					WHILE @y  < @noOfCommas DO 
					   SELECT splitString(idString, ', ', @y) INTO @tempSeparate; 
					   SET  @y = @y + 1; 
                       INSERT INTO tbl_temp_sep_strings(SPLIT_VALUES) values(@tempSeparate);
					END WHILE; 
		END IF; 
END $$
CALL getAllStrings('ab, ac'); -- Call the function like this
/* Now, you have the result, i.e., all the split words in the column SPLIT_VALUES of the tbl_temp_sep_strings
   which you can use by doing a SELECT action. This is helpful as it can be used in SQL IN clauses and other
   similar places where you might be looking for a tuple of values.
                          
   Please note that the table is temporary which is good because then it will get deallocated when the connection
   is closed or the session ends as we wouldn't want a table in our db to persist. You can remove the TEMPORARY keyword
   otherwise.
*/
-- SELECT * FROM sample_database.tbl_temp_sep_strings
                                             
-- BONUS: If a field in some table has mixed values as in single as well as mixed, comma-separated values then you can use the below procedure
DROP PROCEDURE IF EXISTS getIndividualSkills $$
CREATE PROCEDURE cleanMixedUpColumn()
	BEGIN
		SELECT COUNT(DISTINCT infected_column) INTO @noOfSkills FROM sample_database.sample_table WHERE Skill_id IS NOT NULL;
        SET @y1 = 0;
        WHILE @y1  < @noOfSkills DO
					   SET @sql1 = CONCAT('SELECT DISTINCT infected_column INTO @currentValue FROM sample_database.sample_table WHERE infected_column IS NOT NULL ORDER BY infected_column LIMIT 1 OFFSET ' ,@y1,';');
             PREPARE stmt1 FROM @sql1;
					   EXECUTE stmt1;
             DEALLOCATE PREPARE stmt1;
             CALL getAllStrings(@currentValue);
					   SET  @y1 = @y1 + 1;
		END WHILE; 
END $$
DELIMITER ;
CALL cleanMixedUpColumn();