On Sun, Oct 18, 2009 at 10:35 AM, Tim Landscheidt <tim@xxxxxxxxxxxxxxxxxx> wrote: > Daniel Migowski <dmigowski@xxxxxxxxxxx> wrote: > >> I have a very common example which would illustrate the >> above problem a bit more. Guess the following view on a >> company table, which references the country of that company >> in another table. The view itself just returns the >> company-id and the country-name, > >> create view companys_and_countries as >> select company.id, country.name from company left join >> country on (company.country_id = country.id); > >> Pleaso note we have a left join here, so the contents of >> country do by no means affect the contents of the "id" row >> in that view. Lets see what happens when we just query for >> the ids: > >> explain select id from companys_and_countries; > >> The join is done anyway, even if its removed (At least on >> Postgres 8.3). [...] > > How could that be done otherwise? PostgreSQL *must* look at > country to determine how many rows the left join produces. Even if country.id is a primary or unique key? Jeff -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
