Dag �yvind Liodden wrote:
> > > EXPLAIN says (I apologize if this table is hard to read):
> > >
> > > OWNER TABLENAME COLUMN_OR_INDEX STRATEGY
> > > PAGECOUNT
> > > T1 TABLE SCAN
> > > 140
> > > INTERNAL TEMPORARY RESULT EQUAL CONDITION FOR KEY
> > > COLUMN 500
> > > TRADE_ID (USED KEY COLUMN)
> > > T2 NO STRATEGY NOW (ONLY
> > > AT EXECUTION TIME)140
> > > TROODON RESULT IS
> > > COPIED , COSTVALUE IS 1352
> > >
> > > The query runs in about 1,352 seconds (is this what the last
> > > pagecount means?)
> >
> > No, costvalue does NOT mean seconds, it means: expected pages to
> > be read/written.
>
> OK, just a coincidence, then. :) Why does it say "COSTVALUE IS" but no
> real value?
COSTVALUE means the number of pages to read/write.
Noone before really doing it has any idea how many of those pages have to
be read/written physically, how many are in the data cache.
Because of the known difference of time consumption between those two
kinds of reading/writing, no 'real value' in seconds or whatever can be
given.
>
> > > I guess the ideal thing would be if the following had been
> > > possible (but
> > > it's not :):
> > >
> > > select symbol, last(change), last(price), last(trade_time),
> > > last(volume)
> > > from
> > > trade
> > > group by symbol
> >
> >
> > Do you mean select symbol, MAX(change), MAX(price),
> MAX(trade_time) ... ?
>
> No, I want the last change, price and trade_time. With MAX I
> will will get
> the last trade_time (since they are always increasing) but
> not the last
> change and price.
If you want to receive the last trade for each symbol and all
the values stored for this single trade and you know that trade_time
is (of course) increasing then you should use this:
SELECT symbol, change, price, trade_time, volume
FROM trade
WHERE (symbol, trade_time) = ANY
(SELECT symbol, MAX(trade_time)
FROM trade
GROUP BY symbol)
If you have to limit the symbols selected then
BOTH selects should use this limitation, of course at least the top one.
If you want to order them, append for example an ORDER BY change to the
query given above.
Elke
SAP Labs Berlin
_______________________________________________
sapdb.general mailing list
[EMAIL PROTECTED]
http://listserv.sap.com/mailman/listinfo/sapdb.general
