select * from Tg
order by case when exists(select 1 from Tr where gId=Tg.gId) then 1 else 2 end,
(select rDate from Tr where gId=Tg.gId) desc
order by case when exists(select 1 from Tr where gId=Tg.gId) then 1 else 2 end,
(select rDate from Tr where gId=Tg.gId) desc
case
when exists(select gbkId from gbrlasttime where gbkId=guestbook.gbId) then (select gbrlasttime.lasttime from gbrlasttime where gbkId=guestbook.gbId)
else gbDate
end
from guestbook这样写合法吗?谢谢!