On Jul 9, 2007, at 9:22 AM, Gustavo Ces wrote:
Hi all,
I´ve got a strange problem, hope you could help. I´ve got a
table (a ) with n tuples, and two fields , birthplace and birth
date. There´s another table ( say b) with m tuples, where i´ve got
a lot of polygons ( with their code, same as bithplace). Now i want
to make a join, to obtain how many people corresponds to each place-
polygon. I write
create table personsbyplace as select a.birthplacecode as code,count
(*) as peoplecount from a,b where
a.birthplacecode=b.polygoncode group by birthplacecode
Well, what i can´t understand is why "Select sum(count) from
personsbyplace" is > than "a" row number! (n)
In "b" i´ve got all places and "a" table is a list of people, with
their place and birth date. It can´t be greater sum(count) than
number of persons! Where is the mistake?
Probably because there's a duplicated polygonecode (might want to
stick some underscores in the field names so they're easier to read,
btw).
My question is: if you just want a count of people grouped by
birth_place_code, why join to b at all?
--
Jim Nasby jim@xxxxxxxxx
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
