Re: Calculation of unused columns

Daniel Migowski <dmigowski@ikoffice.de> 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.

Tim