On Thursday, February 09, 2012 5:18:19 pm David Salisbury wrote: > On 2/9/12 5:25 PM, Rich Shepard wrote: > > For water quality data the primary key is (site, date, param) since > > there's only one value for a given parameter collected at a specific > > site on > > a single day. No surrogate key needed. > > Yea. I was wondering if the surrogate key debate really boils down to the > composite primary key debate. Seems so in my mind, though one could > maybe come up with a combination. Basically aliases of values and > composite those. Perhaps that's the ultimate methodology. :) > > > The problem with real world data is that different taxonomic levels are > > used. Not all organisms can be identified to species; some (such as the > > round worms, or nematodes) are at the level of order. That means there > > is no > > combination of columns that are consistently not NULL. Sigh. > > I didn't know that about worms. I did know grasses only went to the genus. > You could make a tall skinny self referential table though, and nothing > would be null and everything would be unique ( I think, unless certain > taxon values can appear under different higher order taxon values ). OT. Alright, now I have to ask. When you say grasses(or for that matter round worms) cannot be identified to species are you talking about the data you are receiving or in general. Because as far as I know there are many species identified for both. They are difficult to id but species do exist. > > Thanks for the view points out there. > > Cheers, > > -ds -- Adrian Klaver adrian.klaver@xxxxxxxxx -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
