... ลองใช้คำสั่งข้างล่างน่าจะได้นะครับ ....
select o.vstdate,o.doctor as Doctor_Code,d.name as Doctor_Name,min(s.service5) as 1stPT_Time
from ovst o
left outer join service_time s on s.vn = o.vn
left outer join doctor d on d.code = o.doctor
where o.vstdate between '2009-02-01' and '2009-02-10'
and s.service5 is not null
group by o.vstdate,o.doctor
...
![ยิ้มกว้างๆ :D](https://hosxp.net/smf2/Smileys/default/cheesy.gif)
...