mysql中left join 不一定比 in效率高案例常规来说,left join语法 要比 写 in 效率高,查询快,但是万事有特殊情况,如下sql:DESC SELECT a.business_depart,b.user_id,c.name FROM bocai_ip_list AS a ,bocai_department_admin AS b, bocai_ip_list AS c WHERE b.department_abbr=a.business_depart AND a.id='1057279' AND c.id=b.user_id