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. :-)
--
D'Arcy J.M. Cain <darcy@druid.net> | Democracy is three wolves
http://www.druid.net/darcy/ | and a sheep voting on
+1 416 425 1212 (DoD#0082) (eNTP) | what's for dinner.