题解|拆分| #修复串列了的记录#

SELECT exam_id,
    substring_index(tag, ',', 1) AS tag,
    substring_index(substring_index(tag, ',', 2), ',', -1) AS difficulty,
    CAST( substring_index(tag, ',', -1) AS DECIMAL ) AS duration
FROM examination_info
WHERE tag LIKE '%,%';