Re: Query Assistance

On Wed, 12 Dec 2007 11:58:20 -0500
"Gary Chambers" <gwchamb@gmail.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 (
starttimetimestamp without time zone DEFAULT now() NOT NULL,   -- Timestamp of power on (   endtime timestamp without
timezone,   -- 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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