需求：比如：学校里班级，班级里有学生。利用左连查出所有的信息

select <include refid="Base_Column_List_Left_Join"/>from sys_s_duty_details details left join sys_s_on_duty duty on details.duty_id=duty.idleft join ( select cli.id,cli.name,cli.num,cli.org_id,org.title from sys_client cli left join sys_org org on cli.org_id=org.id) client ondetails.cli_id= client.id

利用左连和子查询。