Re: Views With Unions

Stephan Szabo said:
>
> On Thu, 31 Jul 2003, Christopher Browne wrote:
>
>>   select * from log_table where request_time between 'june 11 2003'
>> and
>>                                                    'june 12 2003';
>>
>> returns a plan:
>> Subquery Scan log_table  (cost=0.00..10950.26 rows=177126 width=314)
>>   ->  Append  (cost=0.00..10950.26 rows=177126 width=314)
>>         ->  Subquery Scan *SELECT* 1  (cost=0.00..3089.07 rows=50307
>> width=71)
>>               ->  Seq Scan on log_table_1  (cost=0.00..3089.07
>> rows=50307 width=71)
>>         ->  Subquery Scan *SELECT* 2  (cost=0.00..602.92 rows=9892
>> width=314)
>>               ->  Seq Scan on log_table_2  (cost=0.00..602.92
>> rows=9892 width=314)
>>         ->  Subquery Scan *SELECT* 3  (cost=0.00..2390.09 rows=39209
>> width=314)
>>               ->  Seq Scan on log_table_3  (cost=0.00..2390.09
>> rows=39209 width=314)
>
> What version are you using?  In 7.3 and up it should be willing to
> consider moving the clause down, unless there's something like a type
> mismatch (because in that case it may not be equivalent without a bunch
> more work on the clause).

That was 7.2.4, although I had also tried it on 7.4 (yesterday's CVS).

Which provides four findings:

1.  On 7.2.4, adding additional type info just doesn't help, fitting with
the notion that, consistent with your comment, improvement wouldn't happen
earlier than 7.3.

There's no help on 7.2 :-(, and the system I'm initially most interested
in using this on is still on 7.2.

2.  When I retried on 7.4, it _did_ find search paths based on Index Scan,
when I added in additional type information.  So the optimization I was
wishing for _is_ there :-).  In the longer term, that's very good news.

3.  I'll have to test this out on 7.3.4, now, as I hadn't, and it sounds
as though that is an interesting case.

4.  It's often necessary to expressly specify type information in queries
to get the optimizer to do the Right Thing.
--
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<http://dev6.int.libertyrms.info/>
Christopher Browne
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