From: Bruce Momjian <maillist@candle.pha.pa.us>
Message-Id: <199805200154.VAA02090@candle.pha.pa.us>
Subject: Re: [DOCS] Re: FE/BE protocol revision patch
To: lockhart@alumni.caltech.edu (Thomas G. Lockhart)
Date: Tue, 19 May 1998 21:54:08 -0400 (EDT)
Cc: tgl@sss.pgh.pa.us, hackers@postgresql.org,
	pgsql-interfaces@postgresql.org (PostgreSQL-interfaces)
In-Reply-To: <35622CED.9B435442@alumni.caltech.edu> from "Thomas G. Lockhart"
	at May 20, 98 01:07:57 am
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> 
> > > 1. Implement addition of atttypmod field to RowDescriptor messages.
> > >    The client-side code is there but ifdef'd out.  I have no idea
> > >    what to change on the backend side.  The field should be sent
> > >    only if protocol >= 2.0, of course.
> 
> Hmm. I was hoping to do something in the backend to allow data types
> like numeric(p,s) which take multiple qualifying arguments (in this
> case, precision and scale). One possibility was to shoehorn both fields
> into the existing atttypmod 16-bit field.
> 
> Seems like atttypmod is now being used for things outside of the
> backend, but I'm not sure how to support these other uses with these
> other possible data types.

We are just passing it back.  There is no special handling of atttypmod
that you need to worry about.  I think we pass it back to Openlink can
know the actual length of the char() and varchar() fields without doing
a dummy select.  However, they better know it is a char()/varchar()
field before using it for such a purpose, because it could be used from
something else later on, as you suggest.

> A better general approach to the type qualifier problem might be to
> define a variable-length data type which specifies column
> characteristics, and then pass that around. For character strings, it
> would have one field, and for numeric() and decimal() it would have two.

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