mysql分隔字符串循环

WITH RECURSIVE split_values (value) AS (
  SELECT SUBSTRING_INDEX('a,b,c,d', ',', 1)
  UNION ALL
  SELECT SUBSTRING_INDEX(SUBSTRING_INDEX('a,b,c,d', ',', numbers.n), ',', -1)
  FROM (SELECT 1 n UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5) numbers
  WHERE numbers.n <= LENGTH('a,b,c,d') - LENGTH(REPLACE('a,b,c,d', ',', '')) + 1
)
SELECT * FROM split_values;

CREATE TEMPORARY TABLE temp_split (value VARCHAR(255));
SET @input = 'a,b,c,d';
SET @pos = 1;
SET @len = LENGTH(@input);

WHILE @pos <= @len DO
  INSERT INTO temp_split (value) VALUES (SUBSTRING(@input, @pos, IF(LOCATE(',', @input, @pos) = 0, @len - @pos + 1, LOCATE(',', @input, @pos) - @pos)));
  SET @pos = IF(LOCATE(',', @input, @pos) = 0, @len + 1, LOCATE(',', @input, @pos) + 1);
END WHILE;

SELECT * FROM temp_split;