Cached in memory is correct as well as the
second statement will only have to process fewer records if the WITH was
done in the first. Breaking up a SELECT statement into 2 parts may be
advantageous, regardless of caching, if there are multiple ANDed WITH
clauses and one or more of them involve translates. For
example:
SSELECT HUGE.ARCHIVE.FILE WITH CUST.ZIP =
"12345" AND WITH PERIOD = "199910"
would be faster as
SELECT HUGE.ARCHIVE.FILE WITH PERIOD =
"199910"
then
SSELECT HUGE.ARCHIVE.FILE WITH CUST.ZIP =
"12345"
assuming that CUST.ZIP is translated and the
PERIOD is a local field. Note the SSELECT in the second statement as
well.
I've often wondered if, when using consecutive
ANDs the filter processor skips the record if the first WITH is false. Why
bother testing the second field if both are ANDed.
my 1 cent.
----- Original Message -----
Sent: Monday, February 02, 2004 11:24
AM
Subject: RE: UDT SELECT
optimization
Chuck,
The order should be immaterial ( it is on every other
database I can think of ).
Just be aware that if you test it by issuing the
commands one after the other, the second may may complete quicker, simply
because the file may be cached in memory.
Brian Leach
Does anyone know whether one of these two
statements is faster?
SELECT FILE BY SOME.DATE WITH SOME.FIELD =
"XXX"
-or-
SELECT FILE WITH SOME.FIELD = "XXX" BY
SOME.DATE
Does the parser / optimizer (if there is one) do
the filter portion of the statement first regardless of the order that you
build it in or does it do things EXACTLY in the order that you enter them
on the command line?
-Chuck
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