test, I didn't run something very
different or some heavy program for all queries. And the result seems
consistent.)
Ubuntu 12.04 LTS
I followed the installation step in Quickstart section of
http://wiki.postgresql.org/wiki/Apt
best regards,
jacket41142
job for entire table of
interested columns, or for each column separately.
regards,
jacket41142
2013/12/11 Jeff Janes
> On Tue, Dec 10, 2013 at 9:28 AM, jacket41142 wrote:
>
>
>>
>> test=> select distinct col_int from t1 group by col_int;
>> Time: 1177.936 ms
>>
筆資料列)
時間: 7063.156 ms
test=> select count(distinct col_int) from t1;
count
---
1025
(1 筆資料列)
時間: 6899.283 ms
I don't think count(*) also uses sort since it should not be needed. But
for the query planner, it seems it can not distinguish between these two
now.
regards,
jacket41142
201
test, I didn't run something very
different or some heavy program for all queries. And the result seems
consistent.)
Ubuntu 12.04 LTS
I followed the installation step in Quickstart section of
http://wiki.postgresql.org/wiki/Apt
best regards,
jacket41142
2013/12/11 Jeff Janes
> On Tuesday, December 10, 2013, jacket41142 wrote:
>
>> Thanks very much.
>>
>> I think another problem is that the cost estimation isn't good enough to
>> reflex real cost. Since we can see, from "explain analyze ...",
>>
