Re: unexpected plan for unused table (8.1dev)

On E, 2005-08-29 at 09:50 +0400, Oleg Bartunov wrote:
> Hi there,
>
> I'm a bit surprised how bad could be plan for unused table.
> I had to cancel second query :)
...
> tp=# explain analyze select tp_rewrite_substitute(query,
> 'select p.name_tsquery, p.name_alias_tsquery from place p')
> from place, to_tsquery('new&york&hotel') as query;
> ^^^^^
>
> Here is plan without analyze:
>
> tp=# explain select tp_rewrite_substitute(query,
> 'select p.name_tsquery, p.name_alias_tsquery from place p')
> from place, to_tsquery('new&york&hotel') as query;

Actually you are asking the query to be evaluated once for each row of
table "place".

> QUERY PLAN
> ---------------------------------------------------------------------------
> Nested Loop (cost=13.50..44280620.90 rows=1964340000 width=32)
> -> Seq Scan on place (cost=0.00..82957.40 rows=1964340 width=0)
> -> Materialize (cost=13.50..23.50 rows=1000 width=32)
> -> Function Scan on query (cost=0.00..12.50 rows=1000 width=32)
> (4 rows)
>
>
>
> The only difference is unused table 'place' in FROM-clause. I typed in by
> mistake, but I think optimizer could figure out not to take into account
> this table.

This is valid SQL and afaik exactly what you asked for in the query.
Postgresql can't possibly know that you made a mistake :)

--
Hannu Krosing <hannu(at)skype(dot)net>