mysql实现类似split

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

SELECT 
    REGEXP_SUBSTR('user1@example.com,user2@example.com,user3@example.com', '[^,]+', 1, LEVEL) AS email
FROM 
    DUAL
CONNECT BY 
    REGEXP_SUBSTR('user1@example.com,user2@example.com,user3@example.com', '[^,]+', 1, LEVEL) IS NOT NULL;

SET @str = 'a,,b,c,,d';
SELECT 
    SUBSTRING_INDEX(SUBSTRING_INDEX(@str, ',', numbers.n), ',', -1) AS 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(REPLACE(@str, ',', 'x')) + 1;