Re: recursive sql

Hi Franz,

It looks like you are trying to solve a comulative sum. You don’t need the lag function, instead you should use sum and you will get a desired result:

Select ts, c, sum(c) over(order by ts) c2 from tt order by ts;

Best,
Igor

> On Aug 9, 2020, at 3:38 AM, Samed YILDIRIM <samed(at)reddoc(dot)net> wrote:
>
> Hi Franz,
>
> Simply you can use window functions[1][2].
>
> pgsql-sql=# select *, lag(c) over (order by ts) as c2 from tt;
> ts | c | c2
> ---------------------+---+----
> 2019-12-31 00:00:00 | 1 |
> 2020-01-01 00:00:00 | 2 | 1
> 2020-07-02 00:00:00 | 3 | 2
> 2020-07-06 00:00:00 | 4 | 3
> 2020-07-07 00:00:00 | 5 | 4
> 2020-07-08 00:00:00 | 6 | 5
> (6 rows)
>
>
> I personally prefer to use window functions due to their simplicity. If you still want to use recursive query: [3]
>
> pgsql-sql=# with recursive rc as (
> select * from (select ts,c,null::numeric as c2 from tt order by ts asc limit 1) k1
> union
> select * from (select tt.ts,tt.c,rc.c as c2 from tt, lateral (select * from rc) rc where tt.ts > rc.ts order by tt.ts asc limit 1) k2
> )
> select * from rc;
> ts | c | c2
> ---------------------+---+----
> 2019-12-31 00:00:00 | 1 |
> 2020-01-01 00:00:00 | 2 | 1
> 2020-07-02 00:00:00 | 3 | 2
> 2020-07-06 00:00:00 | 4 | 3
> 2020-07-07 00:00:00 | 5 | 4
> 2020-07-08 00:00:00 | 6 | 5
> (6 rows)
>
> [1]: https://www.postgresql.org/docs/12/functions-window.html <https://www.postgresql.org/docs/12/functions-window.html>
> [2]: https://www.postgresql.org/docs/12/tutorial-window.html <https://www.postgresql.org/docs/12/tutorial-window.html>
> [3]: https://www.postgresql.org/docs/12/queries-with.html <https://www.postgresql.org/docs/12/queries-with.html>
>
> Best regards.
> Samed YILDIRIM
>
>
>
> 09.08.2020, 09:29, "ml(at)ft-c(dot)de" <ml(at)ft-c(dot)de>:
> Hello,
>
> the table
> create table tt (
> ts timestamp,
> c numeric) ;
>
> insert into tt values
> ('2019-12-31',1), ('2020-01-01',2),
> ('2020-07-02',3), ('2020-07-06',4),
> ('2020-07-07',5), ('2020-07-08',6);
>
> My question: It is possible to get an
> additional column (named c2)
> with
> ( c from current row ) + ( c2 from the previous row ) as c2
>
> the result:
> ts c c2
> .. 1 1 -- or null in the first row
> .. 2 3
> .. 3 6
> .. 4 10
> ...
>
> with recursive ema as ()
> select ts, c,
> -- many many computed_rows
> -- <code> as c2
> from tt -- <- I need tt on this place
>
>
> thank you for help
> Franz
>
>
>