Hi,
If I have a view
like:
create view X as
(
select x from
A
union
all
select x from
B)
and
do
select max(x) from
X
I get a plan
like:
Aggregate
Append
Seq Scan on A
Seq Scan on B
If A and B are
indexed on x, I can get the result much faster as:
select max(x) from
(
select max(x) from
A
union
all
select max(x) from
B) X
with the
plan:
Aggregate
Append
Result
Limit
Index Scan Backward using ..
on A
Result
Limit
Index Scan Backward using ..
on B
My question is
basically why the optimizer doesn't do this? Is it hard, or is it just something
that hasn't been done yet?
My guess is that the
second plan would always be as fast or faster than the first one - even if
A and B wasn't indexed?
Anders
