Re: Explain plan on a Select query

On Mon, Mar 16, 2020 at 12:26 PM John Scalia <jayknowsunix(at)gmail(dot)com> wrote:

> I’m a bit confused on an explain plan I just generated for a select
> statement. The plan’s first line begins with the word “Append” followed by
> the usual (cost....) data. What in the world is an Append doing here? I’ve
> recently performed another analyze on the table, btw.
>

A top level Append would generally be used when you use a UNION ALL, or you
have inheritance.

>
> Also, the query does not seem to be using an index, as the explain shows a
> pair of sequential scans, speaking of which, the second sequential scan
> shows it’s on a table, called <table>_test. Which is a little strange,
> considering that does not exist.
>

Is that the name of the table, or the alias for that table?

"-> Seq Scan on pgbench_accounts pa_alias (cost=0.00..527869.00
rows=20000000 width=97)"

"pgbench_accounts" is the actual table, "pa_alias" is the alias for it.

PostgreSQL will create alias for table when it needs to, but I've never
seen it do so by adding "_test" to the end. Usually it adds "_" and an
integer.

It would really help to be able to see either the plan or the query, or
both.

Cheers,

Jeff