On Oct 12, 2015, at 10:39 AM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> 
> Jeff Janes <jeff.ja...@gmail.com> writes:
>> On Mon, Oct 12, 2015 at 10:58 AM, Israel Brewster <isr...@ravnalaska.net>
>> wrote:
>>> My first thought was to do something like this:
>>> 
>>> SELECT * FROM (SELECT lognum,array_agg(flightnum) as flightnums FROM logs
>>> GROUP BY lognum) s1 WHERE '8%' like ANY(flightnums);
>>> 
>>> But while this doesn't give an error, it also doesn't return any results.
>>> I'm guessing that this is because the wildcard is on the left of the
>>> operator, and needs to be on the right.
> 
>> Right.  The LIKE operator does not have a commutator by default.  (And if
>> you created one for it, it could not use an index in this case.)
> 
> Well, it couldn't use an index anyway, given that the query as written
> wants to collect groups if *any* member is LIKE '8%', rather than
> restricting the data to such flightnums before aggregation occurs.
> 
> Personally I'd suggest building a commutator operator (just need a
> one-liner SQL or plpgsql function as infrastructure) and away you go.

That could work. I'll look into that.

> 
>> I think you're best bet is to do a subquery against the unaggregated table.
> 
>> select * from aggregated a where exists
>>  (select 1 from unaggregated ua where a.lognum=ua.lognum and flightnum
>> like '8%')
> 
> That would work too, but not sure about performance relative to the other
> way.
> 
>                       regards, tom lane


-----------------------------------------------
Israel Brewster
Systems Analyst II
Ravn Alaska
5245 Airport Industrial Rd
Fairbanks, AK 99709
(907) 450-7293
-----------------------------------------------



-- 
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general

Reply via email to