Re: Index/Foreign Key Question

----- Original Message -----
From: "Ron Johnson"
> On Fri, 2003-10-10 at 16:04, David Busby wrote:
> > List,
> >     I'm creating this multi company POS database.
> > My inventory table looks like (all items are unique):
> >
> > id,category_id,invoice_id,x,y,z,gid,uid
> >
> > I have a primary key on id, and then an foreign keys on category_id and
> > invoice_id.
> > GID is the group ID of the company, UID is the companies user, they are
also
> > connected via foreign key to the respective tables.  My question is
this: Do
> > I need to create more indexes on this table when inventory selects look
like
> >
> > select * from inventory where
> >  category_id = 1 and invoice_id is null and gid = 2
> >
> > So where would the indexes need to be placed?  Or since I have the FK
setup
> > are the indexes already in place?  I expect to soon have >500K items in
the
> > inventory table and don't want it to slow down.  I'll have the same type
of
> > issue with clients, invoices, purchase_orders and perhaps more
>
> I'd make a multi-segment (non-unique?) index on:
>    GID
>    CATEGORY_ID
>    INVOICE_ID
>

So the multi column index would be better than the three individual indexes?
Does PostgreSQL only pick one index per table on the select statements?
What about the option of using schemas to segment the data?  That would
eliminate the GID column and help performance correct?  It also means I have
to make company_a.invoice and company_b.invoice tables huh?

/B