Hi,
On Fri, Feb 2, 2018 at 9:28 PM, David G. Johnston
wrote:
> You probably can (I assume the nulls aspect of the index doesn't prevent PK
> usage), but you must add the PK to the table after creating the index and
> not let the system auto-generate the index for you.
>
> https://www.postgresql.
On Fri, Feb 2, 2018 at 8:49 AM, Nandakumar M wrote:
> But, for the PK column we are not in control of the index that is created.
>
You probably can (I assume the nulls aspect of the index doesn't prevent
PK usage), but you must add the PK to the table after creating the index
and not let the sy
Hi,
On Fri, Feb 2, 2018 at 8:30 PM, Tom Lane wrote:
>
> The planner does not consider this and it doesn't really seem like
> something worth expending cycles on. If you know that there won't be
> nulls in the column, why are you insisting on specifying a nondefault
> value of NULLS FIRST/LAST in
Nandakumar M writes:
> The order by column has a not null constraint on it and so nulls last or
> first shouldn't make any difference.
The planner does not consider this and it doesn't really seem like
something worth expending cycles on. If you know that there won't be
nulls in the column, why
Hi,
On 2 Feb 2018 15:06, "Laurenz Albe" wrote:
>In the above case, the optimizer does >not know that it will get the rows
>in the correct order: indexes are >sorted ASC NULLS LAST by default,
>so a backwards index scan will >produce the results NULLS FIRST,
>which is the default for ORDER BY ..
I did some more tests. I've made an SQL dump of the table. Then used
head/tail commands to cut the data part. Then used shuf command to
shuffle rows, and then joined the pieces back and restored the table
back into DB.
Before:
select array_agg(aid) from (select aid from pgbench_accounts order
On Thu, 2018-02-01 at 20:00 +0530, Nandakumar M wrote:
> Hi,
>
> I am using Postgres version 9.4.4 on a Mac machine.
> I have 2 queries that differ only in the order by clause.
> One of it has 'nulls last' and the other one does not have it.
> The performance difference between the two is consider
tor 2018-02-01 klockan 20:34 + skrev Johan Fredriksson:
> > Johan Fredriksson writes:
> > > Bad plan: https://explain.depesz.com/s/avtZ
> > > Good plan: https://explain.depesz.com/s/SJSt
> > > Any suggestions on how to make the planner make better decisions
> > > for
> > > this query?
> >
> >
