Mark Pasterkamp writes:
> I am comparing two queries, q1 and q2 respectively.
> Query q1 is the original query and q2 is an attempt to reduce the cost of
> execution via leveraging the materialized view ci_t_15.
> ...
> Running explain analyze on both queries I get the following execution plans.
On Fri, Aug 16, 2019 at 12:16 AM <066ce...@free.fr> wrote:
> Generally speaking, when executing UNION ; a DISTINCT is run afterward on
> the resultset.
>
> So, if you're sure that each part of UNION cannot return a line returned
> by another one, you may use UNION ALL, you'll cut the cost of the
Generally speaking, when executing UNION ; a DISTINCT is run afterward on the
resultset.
So, if you're sure that each part of UNION cannot return a line returned by
another one, you may use UNION ALL, you'll cut the cost of the final implicit
DISTINCT.
- Mail original -
De: "Mark
Mark Pasterkamp writes:
> I was wondering if someone could help me understands what a union all
> actually does.
Generally speaking, it runs the first query and then the second query.
You'd really need to provide a lot more detail for anyone to say more
than that.
