Another planner/optimizer question...

Once again, a slightly convoluted question, but it seems that PG may be
doing a little more work than is necessary when selecting from views with
sub-selects. It seems that every time a view field is being referenced in
an outer select expression, the view field is being re-evaluated. Is there
any way to get PG to know that it only needs to do the aggregate once?

eg.

create table b(f1 int, f2 int);
create table r(f1 int);

create view bv as select f1,f2,
exists(select * from r where r.f1=b.f1) as has_f1,
exists(select * from r where r.f1=b.f2) as has_f2
from b;

explain select f1,f2,
case when has_f1 and has_f2 then 'both'
when has_f1 then 'f1_only'
when has_f2 then 'f2_only'
else 'none'
end as status
from bv;

Seq Scan on b (cost=0.00..20.00 rows=1000 width=8)
SubPlan
-> Seq Scan on r (cost=0.00..22.50 rows=5 width=4)
-> Seq Scan on r (cost=0.00..22.50 rows=5 width=4)
-> Seq Scan on r (cost=0.00..22.50 rows=5 width=4)
-> Seq Scan on r (cost=0.00..22.50 rows=5 width=4)

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