Re: nth_value and row_number in a partition

Hi

I think you can do this without any need to use nth_value.
Only first_value and current v2 is needed.

select roads, orders, v1, v2, segment,
first_value(v1) over(partition by roads, segment order by roads, orders)
- v2
from test order by roads, orders;

The point is to define the partition by roads and segment but to order
it via roads and orders.

Regards Martin

Am 25.01.2018 um 21:52 schrieb Olivier Leprêtre:
>
> Hi Martin,
>
> Here is an example in a "excel view". Red value are first value. 3
> partitions defined by roads and segment columns.
>
> The goal is to substract v2 (D) from v1 first value for each window.
> Hope this is clear enough.
>
> Davir, you're right, imbricated is my bad translation for nested.
>
>
>
>
> A
>
>
>
> B
>
>
>
> C
>
>
>
> D
>
>
>
> E
>
>
>
> F
>
>
>
> 1
>
>
>
> roads
>
>
>
> orders
>
>
>
> v1
>
>
>
> v2
>
>
>
> v3
>
>
>
> segment
>
>
>
> v3 calculation
>
> 2
>
>
>
> 41
>
>
>
> 1
>
>
>
> 632
>
>
>
> 0
>
>
>
> 632
>
>
>
> 1055
>
>
>
> C2-D2
>
> 3
>
>
>
> 41
>
>
>
> 2
>
>
>
> 632
>
>
>
> 0
>
>
>
> 632
>
>
>
> 1055
>
>
>
> C2-D3
>
> 4
>
>
>
> 41
>
>
>
> 3
>
>
>
> 600
>
>
>
> 16
>
>
>
> 616
>
>
>
> 1055
>
>
>
> C2-D4
>
> 5
>
>
>
> 41
>
>
>
> 4
>
>
>
> 70
>
>
>
> 25
>
>
>
> 607
>
>
>
> 1055
>
>
>
> C2-D5
>
> 6
>
>
>
> 41
>
>
>
> 5
>
>
>
> 60
>
>
>
> 30
>
>
>
> 30
>
>
>
> 1041
>
>
>
> C6-D6
>
> 7
>
>
>
> 41
>
>
>
> 6
>
>
>
> 64
>
>
>
> 3
>
>
>
> 57
>
>
>
> 1041
>
>
>
> C6-D7
>
> 8
>
>
>
> 41
>
>
>
> 7
>
>
>
> 14
>
>
>
> 2
>
>
>
> 12
>
>
>
> 1042
>
>
>
> C8-D8
>
> 9
>
>
>
> 41
>
>
>
> 8
>
>
>
> 2
>
>
>
> 6
>
>
>
> 8
>
>
>
> 1042
>
>
>
> C8-D9
>
> Thanks very much for your help
>
> *De :*Martin Stöcker [mailto:martin(dot)stoecker(at)stb-datenservice(dot)de]
> *Envoyé :* jeudi 25 janvier 2018 21:13
> *À :* Olivier Leprêtre <o(dot)lepretre(at)gmail(dot)com>;
> pgsql-sql(at)lists(dot)postgresql(dot)org
> *Objet :* Re: nth_value and row_number in a partition
>
> Hi Olivier
>
> can you please give me the structure of your table, maybee some sample
> data too.
> And please describe in words not in SQL your calculation.
>
> Regards Martin
>
> Am 25.01.2018 um 20:49 schrieb Olivier Leprêtre:
>
> Hi David,
>
> Thanks for your answer, I tried your suggestion as well as many
> other combinations, no success. Here are some of them. I just
> don't understand which syntax is required
>
> select roads,orders,(first_value(v1)
>
> over (partition by roads,segment order by
> orders)-(nth_value(v2,cast(row_number() over (partition by
> roads,*order *by orders)  as integer)) over (partition by
> roads,segment order by orders))) as result
>
> from mytable
>
> or
>
> select roads,orders,(first_value(v1)
>
> over (partition by roads,segment order by
> orders)-(nth_value(v2,row_number() over (partition by
> roads,*order* by orders)::integer)) over (partition by
> roads,segment order by orders))) as result
>
> from mytable
>
> >>syntax error near order (bold)
>
> select roads,orders,(first_value(v1)
>
> over (partition by roads,segment order by
> orders)-(nth_value(v2,row_number() over (partition by
> roads)::integer)) *over* (partition by roads,segment order by
> orders))) as result
>
> from mytable
>
> >> syntax error near over
>
> select roads,orders,(first_value(v1)
>
> over (partition by roads,segment order by
> orders)-nth_value(v2,row_number() over (partition by
> roads)::integer) over (partition by roads,segment order by
> orders)) as result
>
> from mytable
>
> >> window call cannot be imbricated
>
> select roads,orders,(first_value(v1)
>
> over (partition by roads,segment order by
> orders)-nth_value(v2,row_number()  over (partition by
> roads,segment order by orders)::integer)) as result
>
> from mytable
>
> >> nth_value requires an over clause
>
> select roads,orders,(first_value(v1)
>
> over (partition by roads,segment order by
> orders)-nth_value(v2,row_number()::integer) over (partition by
> roads,segment order by orders)) as result
>
> from mytable
>
> >> row_number requires an over clause
>
> *De :* David G. Johnston [mailto:david(dot)g(dot)johnston(at)gmail(dot)com]
> *Envoyé :* jeudi 25 janvier 2018 19:44
> *À :* Olivier Leprêtre <o(dot)lepretre(at)gmail(dot)com>
> <mailto:o(dot)lepretre(at)gmail(dot)com>
> *Cc :* pgsql-sql(at)lists(dot)postgresql(dot)org
> <mailto:pgsql-sql(at)lists(dot)postgresql(dot)org>
> *Objet :* Re: nth_value and row_number in a partition
>
> On Thursday, January 25, 2018, Olivier Leprêtre
> <o(dot)lepretre(at)gmail(dot)com <mailto:o(dot)lepretre(at)gmail(dot)com>> wrote:
>
> nth_value(integer, bigint) doesn't exists.
>
> This is close, you just need to cast to integer.
>
> (cast(row_number() as integer)  over (partition by
> roads,segments order by orders)))
>
> You cannot separate the window function from its over clause.
>
> Cast( Row_number() over (...) as integer )
>
> Not tested...and I tend to use :: instead of cast
>
> David J.
>

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