Re: nextval per counted

On Fri, Jan 27, 2023 at 2:25 PM Rob Sargent <robjsargent(at)gmail(dot)com> wrote:

> On 1/27/23 14:20, David G. Johnston wrote:
>
> On Fri, Jan 27, 2023 at 1:59 PM Rob Sargent <robjsargent(at)gmail(dot)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.