mysql的split函数

SELECT SUBSTRING_INDEX(SUBSTRING_INDEX('a,b,c,d', ',', n), ',', -1) AS element
FROM (
    SELECT 1 AS n UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4
) AS numbers
WHERE n <= LENGTH('a,b,c,d') - LENGTH(REPLACE('a,b,c,d', ',', '')) + 1;

SELECT REGEXP_SUBSTR('a,b,c,d', '[^,]+', 1, n) AS element
FROM (
    SELECT 1 AS n UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4
) AS numbers
WHERE n <= REGEXP_COUNT('a,b,c,d', '[^,]')+1;

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', ',', n) AS element
FROM (
    SELECT 1 AS n UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4
) AS numbers
WHERE n <= LENGTH('a,b,c,d') - LENGTH(REPLACE('a,b,c,d', ',', '')) + 1;