mysql 字符串分割成数组

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

SELECT * FROM (
    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
) AS t;

SET @json = '["a", "b", "c", "d"]';
SELECT JSON_UNQUOTE(JSON_EXTRACT(@json, CONCAT('$[', idx, ']'))) AS val
FROM (
    SELECT 0 idx UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4
) AS idx
WHERE idx < JSON_LENGTH(@json);