大数据量查询

 select ...
from A,
B,
C,
D,
E1
where (condition on E1)
and (joins and other conditions)

union
select ...
from A,
B,
C,
D,
E2
where (condition on E2)
and (joins and other conditions)   

select ...
from A,
B,
C,
D,
(select ...
from E1
where (condition on E1)
union
select ...
from E2
where (condition on E2)) E
where (joins and other conditions)    

select c.custname, o.ordid, os.status, os.statusdate
from customers c,
orders o,
orderstatus os
where o.ordid = os.ordid
and not exists (select null
from orderstatus os2
where os2.status = 'COMPLETE'
and os2.ordid = o.ordid)
and os.statusdate = (select max(statusdate)
from orderstatus os3
where os3.ordid = o.ordid)
and o.custid = c.custid   

and (o.ordid, os.statusdate) = (select ordid, max(statusdate)
from orderstatus
group by ordid)   

and (os.ordid, os.statusdate) = (select ordid, max(statusdate)
from orderstatus
group by ordid)  

select c.custname, o.ordid, os.status, os.statusdate
from customers c,
orders o,
orderstatus os,
(select ordid, max(statusdate) laststatusdate
from orderstatus
group by ordid) x
where o.ordid = os.ordid
and not exists (select null
from orderstatus os2
where os2.status = 'COMPLETE'
and os2.ordid = o.ordid)
and os.statusdate = x.laststatusdate
and os.ordid = x.ordid
and o.custid = c.custid    

select c.custname, o.ordid, os.status, os.statusdate
from customers c,
orders o,
orderstatus os,
(select ordid, max(statusdate) laststatusdate
from orderstatus
group by ordid) x
where o.ordid = os.ordid
and os.statusdate = x.laststatusdate
and os.ordid = x.ordid
and os.status != 'COMPLETE'
and o.custid = c.custid