001.mysql-炸裂函数的实现

 

SELECT
    substring_index(substring_index(a.chain,'_',b.help_topic_id + 1    ),    '_' ,- 1    ) AS ID
FROM
    (select '1_11_1223_1242' as chain) a  
JOIN mysql.help_topic b ON b.help_topic_id <
(length(a.chain) - length( replace(a.chain, '_', '')  ) + 1)