Обсуждение: nextval per counted

with husb as(
select e.ma, count(distinct coalesce(e.pa, nextval('egogen')::text)) as mates
from emp_all_by3 e group by e.ma order by mates
)
select mates, count(*)
from husb
group by mates order by mates desc;

with husb as(
  select e.ma, count(distinct coalesce(e.pa, nextval('egogen')::text)) mates
  from emp_all_by3 e
  where ma is not null
  group by e.ma order by mates
)
select mates, count(*) from husb group by mates order by mates desc;

with husb as(
  select e.ma, coalesce(e.pa,'fix') as pa
  from emp_all_by3 e
  where e.ma is not null
),
fixed as (
  select e.ma, count(distinct e.pa) mates
  from husb e group by e.ma order by mates
)
select mates, count(*) from fixed group by mates order by mates desc;

On Fri, Jan 27, 2023 at 1:59 PM Rob Sargent <robjsargent@gmail.com> wrote:

I'm trying to craft SQL to invoke a sequence nextval once per grouped value.

This seems like a very unusual usage of nextval/sequences...

with cleanup as (

  select DISTINCT e.ma, coalesce(e.pa, 'fix') as pa from ...

), compute as (

  select ma, pa, nextval(...) from cleanup

)

select * from compute ... -- do whatever else you want

So far I have this:

with husb as(
select e.ma, count(distinct coalesce(e.pa, nextval('egogen')::text)) as mates
from emp_all_by3 e group by e.ma order by mates
)
select mates, count(*)
from husb
group by mates order by mates desc;

Your "order by mates" in the CTE is totally pointless and wasting resources.

David J.

On Fri, Jan 27, 2023 at 2:25 PM Rob Sargent <robjsargent@gmail.com> wrote:

On 1/27/23 14:20, David G. Johnston wrote:

On Fri, Jan 27, 2023 at 1:59 PM Rob Sargent <robjsargent@gmail.com> wrote:

I'm trying to craft SQL to invoke a sequence nextval once per grouped value.

This seems like a very unusual usage of nextval/sequences...

with cleanup as (

  select DISTINCT e.ma, coalesce(e.pa, 'fix') as pa from ...

), compute as (

  select ma, pa, nextval(...) from cleanup

)

select * from compute ... -- do whatever else you want

So far I have this:

with husb as(
select e.ma, count(distinct coalesce(e.pa, nextval('egogen')::text)) as mates
from emp_all_by3 e group by e.ma order by mates
)
select mates, count(*)
from husb
group by mates order by mates desc;

Your "order by mates" in the CTE is totally pointless and wasting resources.

David J.

Yeah, it wasn't when that was the last bit executed...

Seems asking a sequence for an id isn't too unusual?  Or are they specifically intended for primary keys?

Yes, their design is excellent for surrogate primary keys.  I don't even know what to call what you are doing but it isn't that.  It seems like some form of counting but stuff like "row_number" and "count" perform that function.  I don't think I'd trust using them as a counter...for that I'd do counting in the query then have a separate aspect, in user-space, not the system catalogs, that increments a counter.

David J.