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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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