mysql实现split作用

SELECT 
    SUBSTRING_INDEX(SUBSTRING_INDEX('a,b,c,d', ',', numbers.n), ',', -1) AS split_value
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 
    REGEXP_SUBSTR('a,b,c,d', '[^,]+', 1, LEVEL) AS split_value
FROM 
    DUAL
CONNECT BY 
    LEVEL <= 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', ',', 1); -- 输出 'a'
SELECT SPLIT_STR('a,b,c,d', ',', 2); -- 输出 'b'
SELECT SPLIT_STR('a,b,c,d', ',', 3); -- 输出 'c'
SELECT SPLIT_STR('a,b,c,d', ',', 4); -- 输出 'd'