It's just version 0.1 but it looks very good IMO. From the READmE:

GtkSQL v0.1 - 02 May 1998
=========================
  by Lionel ULMER (bbrox@mygale.org)

  GtkSQL is a graphical query tool for PostgreSQL 6.3. I've written it
to learn how to use Gtk, and this version is quite unpolished (it
lacks several features I plan to add), but as it is quite stable and
usable in its present state, I decided to release it now :-).
  A list of changes from version 0.0 is in the Changelog file. Feel
free to mail me for any comments / questions / bug reports /
improvements requests you have (I LOVE mail :-)).

  There is a home page for GtkSQL :
     http//www.mygale.org/~bbrox/GtkSQL/

Michael
-- 
Dr. Michael Meskes, Project-Manager    | topsystem Systemhaus GmbH
meskes@topsystem.de                    | Europark A2, Adenauerstr. 20
meskes@debian.org                      | 52146 Wuerselen
Go SF49ers! Go Rhein Fire!             | Tel: (+49) 2405/4670-44
Use Debian GNU/Linux!                  | Fax: (+49) 2405/4670-10

Tue, 19 May 1998 12:36:09 +0200 (CEST)
Michael Meskes <meskes@topsystem.de>
Anyone seen gtksql?