RE: nth_value and row_number in a partition

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.

Thanks very much for your help

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

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.g.johnston@gmail.com]
Envoyé : jeudi 25 janvier 2018 19:44
À : Olivier Leprêtre <o.lepretre@gmail.com>
Cc : pgsql-sql@lists.postgresql.org
Objet : Re: nth_value and row_number in a partition

 

On Thursday, January 25, 2018, Olivier Leprêtre <o.lepretre@gmail.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.