Re: [HACKERS] create view as select distinct (fwd)

Oleg Broytmann wrote:

>
> Hello!
>
> VIEW on 6.4.2 ignores DISTINCT. Is it a bug? known?
>

It's a known missing feature (not a bug - more like a design
fault).

DISTINCT is implemented as a unique sort step taken over the
final result of a query. Views are implemented via the query
rewrite rule system. If now someone would define a DISTINCT
view and selects a join of it with another table, the rewrite
system cannot tell the planner that only the scan's resulting
from the view should be sorted unique. It could only tell
that the entire result should be DISTINCT - what's wrong - so
I left it out.

I'm planning to implement some kind of subquery rangetable
entries someday. At that time, all these problems (DISTINCT,
GROUP BY, ORDER BY) of views will disappear.

Jan

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