mysql 字符串分割循环

DELIMITER $$

CREATE FUNCTION SPLIT_STR(
  x VARCHAR(255),
  delim VARCHAR(12),
  pos INT
)
RETURNS VARCHAR(255)
DETERMINISTIC
BEGIN
  RETURN REPLACE(SUBSTRING(SUBSTRING_INDEX(x, delim, pos),
         LENGTH(SUBSTRING_INDEX(x, delim, pos - 1)) + 1),
         delim, '');
END$$

DELIMITER ;

SELECT SPLIT_STR('a,b,c,d', ',', 2); -- 返回 'b'

SELECT 
  SUBSTRING_INDEX(SUBSTRING_INDEX('a,b,c,d', ',', numbers.n), ',', -1) AS val
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;