Re: Suppressing unused subquery output columns

On Thu, Jun 5, 2014 at 10:27 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> I'm not entirely convinced that it's worth the extra planning cycles,
> though. Given the small number of complaints to date, it might not
> be worth doing this. Thoughts?
>

Would this avoid execution of expensive functions in views when their
output is discarded?

-- On 9.3
CREATE TABLE data (col1 serial primary key);
INSERT INTO data DEFAULT VALUES;
INSERT INTO data DEFAULT VALUES;

CREATE OR REPLACE VIEW v AS select *, (pg_sleep(1))::text FROM data;

t=# explain analyze select col1 from v;
QUERY
PLAN
--------------------------------------------------------------------------------------------------------------
Subquery Scan on v (cost=0.00..76.00 rows=2400 width=4) (actual
time=1001.086..2002.217 rows=2 loops=1)
-> Seq Scan on data (cost=0.00..52.00 rows=2400 width=4) (actual
time=1001.083..2002.210 rows=2 loops=1)
Total runtime: 2002.268 ms
(3 rows)

regards,

Rod