mysql中split函数用法

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 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 value
FROM 
    dual
CONNECT BY 
    REGEXP_SUBSTR('a,b,c,d', '[^,]+', 1, level) IS NOT NULL;

SELECT 
    JSON_EXTRACT(json_array, CONCAT('$[', idx, ']')) AS value
FROM 
    (SELECT '["a","b","c","d"]' AS json_array) t,
    (SELECT @rownum:=@rownum+1 AS idx FROM (SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4) r, (SELECT @rownum:=0) n) idx
WHERE 
    idx < JSON_LENGTH(json_array);