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From: manatt@sirius.llnl.gov (Doug Manatt)
Newsgroups: comp.databases
Subject: Re: Optimal SQL query needed
Keywords: SQL supersede timestamps
Message-ID: <93266@lll-winken.LLNL.GOV>
Date: 15 Mar 91 23:19:41 GMT
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Organization: Lawrence Livermore National Labs, Livermore CA
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In article <13659@blia.sharebase.com>, miket@blia.sharebase.com (Mike Tossy) writes:
>In article <1991Mar13.224746.5293@qualcomm.com>, greg@harvey.qualcomm.com (greg Noel) writes:
>> ...
>>Intuitivly, what I would like to tell
>>the data base engine is to look up all records with the same value of A riffle
>> through them, and select the one with the largest B.C value.
>>...
>> Is there a way to do do the query more optimally or to do the whole query in
>> one request, so that the execptions don't need to be handled by the program?
>...
>I suggest that the solution is to add another column B'.  Column B is the
>time the record became active and B' is the time the record became inactive


	The quick and cheap solution is to add a 1 byte boolean column that
	tells only if the record is currently valid or invalid.  In our
	design, many of our timestamped entries have a supercede column
	that takes on the two values ("T" or "F") and when an existing entry
	is updated all "F"s are changed to "T"s before the insert.


		Doug Manatt
		Lawrence Livermore Natl Lab
		Human -- (415) 422-7257  FAX -- (415) 422-3160
		manatt@lll-winken.llnl.gov
--
		Doug Manatt
		Lawrence Livermore Natl Lab
		Human -- (415) 422-7257  FAX -- (415) 422-3160
		manatt@lll-winken.llnl.gov