MYSQL字符数字混合排序，类似书的章节目录排序

上sql

SELECT serial_number serialNum,
CAST(SUBSTRING_INDEX(serial_number,'.',1) AS UNSIGNED) AS grade_1,
IF((LENGTH(serial_number)-LENGTH(REPLACE(serial_number,'.','')))>=1 ,CAST(SUBSTRING_INDEX(SUBSTRING_INDEX(serial_number,'.',2),'.',-1) AS UNSIGNED),0) AS grade_2,
IF((LENGTH(serial_number)-LENGTH(REPLACE(serial_number,'.','')))>=2 ,CAST(SUBSTRING_INDEX(SUBSTRING_INDEX(serial_number,'.',3),'.',-1) AS UNSIGNED),0) AS grade_3


FROM `t_knowledge_node` WHERE knowledge_tree_id=407 AND `level`<=4
AND invalid_flag=0 AND delete_flag= 0 
ORDER BY 
grade_1,grade_2,grade_3

效果：