Re: Query Assistance

On Wed, 12 Dec 2007 11:58:20 -0500
"Gary Chambers" <gwchamb(at)gmail(dot)com> wrote:
> All...
>
> I have a simple table in PostgreSQL 8.2.5:
>
> CREATE TABLE power_transitions (
> -- Transition ID (PK)
> tid integer NOT NULL,
> -- State ID (0 = Unknown, 1 = Online (AC power), 2 = Offline (Battery)
> sid smallint NOT NULL,
> -- Timestamp of transition
> statetime timestamp without time zone DEFAULT now() NOT NULL,
> -- Is this a real outage?
> is_outage boolean DEFAULT true NOT NULL
> );
>
> It contains a log of power outages (transitions). I'd like to create
> query that returns a transition offline time and associated return to
> online time. Is there a better way of handling this? I am open to
> schema change suggestions. Thanks very much!

Have you considered this?

CREATE TABLE power_transitions (
-- Transition ID (PK)
tid integer NOT NULL,
-- Timestamp of power off (
starttime timestamp without time zone DEFAULT now() NOT NULL,
-- Timestamp of power on (
endtime timestamp without time zone,
-- Is this a real outage? may not be needed.
is_outage boolean DEFAULT true NOT NULL
);

The is_outage bool could be handled with special timestamps (e.g.
EPOCH) but I am not sure what it signifies to you. Of course you have
to deal with false transitions but I don't know what your information
capture system is so I can't work out all the details but this seems
like a good base for what you want. Every row that has a valid start
and end time is a complete record of an outage.

I am also thinking of a scheme that uses two tables but I don't really
know your environment or requirements. I am assuming that you spend
more time querying the table than updating it. If not your problem
isn't your database, it's your power plant. :-)

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