Message-ID: <BLU0-SMTP934181715239A633CC970AAC6B0@phx.gbl>
Date: Sun, 03 Oct 2010 14:54:41 -0400
From: Frank Bax <fbax@sympatico.ca>
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To: pgsql-sql@postgresql.org
Subject: join returns too many results...
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When I join tables; I will sometimes get multiple rows back as in this 
example.

create table class(name varchar, p point, d int);
insert into class values( 'All', point(50,50), 100 );
insert into class values( 'NE70', point(70,70), 20 );
insert into class values( 'NE75', point(75,75), 20 );
insert into class values( 'NE80', point(80,80), 20 );
insert into class values( 'Centre', point(50,50), 5 );

create table list(x varchar, p point);
insert into list values('A',point(10,10));
insert into list values('B',point(75,75));
insert into list values('C',point(51,51));

select x,name,class.p<->list.p as dist, class.d as size from list left 
join class on list.p <@ circle(class.p,class.d);
  x |  name  |       dist       | size
---+--------+------------------+------
  A | All    | 56.5685424949238 |  100
  B | All    | 35.3553390593274 |  100
  B | NE75   |                0 |   20
  B | NE70   | 7.07106781186548 |   20
  B | NE80   | 7.07106781186548 |   20
  C | All    |  1.4142135623731 |  100
  C | Centre |  1.4142135623731 |    5

In the case where multiple rows are returned from class; I will need to 
add another condition which decides which row to return.
1) distance from centre
2) size of circle
Whatever clause I choose to add I *must* ensure that final result set 
contains only one-to-one join between tables.  Either of these two 
results is acceptable:

For option 1; result C=All or C=Centre is acceptable.
For option 2; result B=NE70 or B=NE75 or B=NE80 is acceptable.

I am lost trying to construct SQL to accomplish this...