From: Date: April 1 2006 4:59pm
Subject: getting table meta data (primary key, in this case)
List-Archive: http://lists.mysql.com/internals/33492
Message-Id: <20060401145900.GK1596@w3.org>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
	protocol="application/pgp-signature"; boundary="DN8g+DOX2TxGxleI"

--DN8g+DOX2TxGxleI
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

How can I, during query parsing on the server, efficiently find what
field is labeled as a primary key for a given table?

Why:
SPARQL is a graph-based query language and doesn't (ideally) worry
about how the links in the graph are constructed. The obvious mapping
for the SPARQL query
  SELECT ?apt WHERE { <Orders.id=3D2186> <Orders.shippingAddress> ?d .
		      ?d               <Addresses.apt>          ?apt };
is
  SELECT Addresses_0.apt
    FROM Orders AS Orders_0
    JOIN Addresses as Addresses_0
         ON Orders_0.shippingAddress=3DAddresses_0.id
   WHERE Orders_0.id=3D3183;

The missing piece of info is that the Orders.shippingAddress is a
foreign key for Addresses.id . For simplicity on the first round, I'm
assuming:
  1 tuple identifiers are "primary keys" and are one field wide
  2 tuple references are "foreign keys" and are one field wide
  3 all tuple references to a table reference the same identifier

Encountering ?d a second time in the query allows me to infer that
Orders.shippingAddress is a foreign key to Addresses. I just need to
pull "id" out of the air, or better yet, out of the table meta data.

I have only seen this done when the client asks the question, which it
does with a particular query. I'm hoping not to have to do a query
while parsing, but will if I have to. I currently share no info
between queries. (how do I do that, anyways?)

For more info on this, see
  http://www.w3.org/2005/05/22-SPARQL-MySQL/
  http://www.w3.org/2003/01/21-RDF-RDB-access/
--=20
-eric

office: +81.466.49.1170 W3C, Keio Research Institute at SFC,
                        Shonan Fujisawa Campus, Keio University,
                        5322 Endo, Fujisawa, Kanagawa 252-8520
                        JAPAN
        +1.617.258.5741 NE43-344, MIT, Cambridge, MA 02144 USA
cell:   +81.90.6533.3882

(eric@stripped)
Feel free to forward this message to any list for any purpose other than
email address distribution.

--DN8g+DOX2TxGxleI
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature
Content-Disposition: inline

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.1 (GNU/Linux)

iQEVAwUBRC6VNJZX2p1ccTnpAQIf8Af/dZ9S0F83CUeP2ynANP3Zr6vJOmvhQhXe
MTFB9dSu/aQCGS+3dyJOnG3OvmPYY0t5Q+mxIGvvBda1ydlKpteQ1smc+uOeQ05d
h3lb5r6m1b4c46oJwwp4wT2Gxt/mcGI6Tv24rWHvvyKg1gYSxpT3XlaB5WY20Ald
L3ECHoPlYvtPXmEJDQdh910CZ7HKwkUskRfWbrThnmbhepQmkiee+/OcpyjuI6iX
lcUUQF7YS0Ek6soJMJCmGiurzV4+X4IcuYA36huEIFrEOppIWWvKhxTHp4hIYwkA
Pck4hd5u1Q/q/MP0w5B3dGc58h+FBWBXNeyjQ369zDLYDAU1ythpbg==
=WofM
-----END PGP SIGNATURE-----

--DN8g+DOX2TxGxleI--