Re: UNION ALL

2019-08-16 Thread Tom Lane
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.

Re: UNION ALL

2019-08-16 Thread Mark Pasterkamp
First of all, thank you for the replies. I am using a base installation of postgres 10.10, with no modifications to any of the system defaults. I am trying to speedup a join between two tables: the title table and the cast_info table. The title table is a table containing information about

Re: UNION ALL

2019-08-15 Thread Ibrar Ahmed
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

Re: UNION ALL

2019-08-15 Thread 066ce286
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

Re: UNION ALL

2019-08-15 Thread Tom Lane
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.