Re: Selecting a constant question

> -----Original Message-----
> From: pgsql-hackers-owner@postgresql.org [mailto:pgsql-hackers-
> owner@postgresql.org] On Behalf Of Dann Corbit
> Sent: Monday, June 11, 2007 1:52 PM
> To: Martijn van Oosterhout
> Cc: pgsql-hackers@postgresql.org
> Subject: Re: [HACKERS] Selecting a constant question
>
> > -----Original Message-----
> > From: Martijn van Oosterhout [mailto:kleptog@svana.org]
> > Sent: Monday, June 11, 2007 1:46 PM
> > To: Dann Corbit
> > Subject: Re: [HACKERS] Selecting a constant question
> >
> > On Mon, Jun 11, 2007 at 01:29:37PM -0700, Dann Corbit wrote:
> > > Our application is using the libPQ interface to access postgres.
> > >
> > > The query is "select '123' from <tablename>"  .. the table is not
> > > important.
> > >
> > > After executing the query, we interrogate the metadata of the
result
> set
> > > using the PQfsize, PQfmod and PQftype functions.
> >
> > Did you read the documentation of the PQfsize function?
> >
> > PQfsize returns the space allocated for this column in a database
row,
> > in other words the size of the server's internal representation of
the
> > data type. (Accordingly, it is not really very useful to clients.) A
> > negative value indicates the data type is variable-length.
> >
> >
>
http://www.postgresql.org/docs/8.2/interactive/libpq-exec.html#LIBPQ-EXE
> C-
> > SELECT-INFO
> >
> > > The size of the column is returned as 65534  (or -2 if you
consider
> this
> > > a signed short value)
> >
> > It's variable length, you can't say anything more.
>
> So what you are saying is that the constant '1' is variable length,
and
> there is no way to find out the maximum length from the database.

I have a PostgreSQL feature request:

Report the maximum size of a variable length string from the server.

Surely, we cannot be the only people who will need this information.  If
(for example) someone wants to bind to a grid, then the maximum size has
to be known in advance.