mysql 根据父节点查询下面所有子节点-根据节点等级升序

SELECT c3.id FROM ( SELECT c1.id,c1.parent_id, IF( find_in_set( c1.parent_id, @p ) > 0, @p := concat( @p, ‘,’, c1.id ), 0 ) AS childIds FROM ( SELECT c.id,c.parent_id FROM crm_project_category c WHERE c.dept_id = #{deptId} and c.delete_flag =0 ORDER BY c.id ) c1, ( SELECT @p := #{parentId} ) c2 ) c3 WHERE c3.childIds != 0 order by category_level