Re: I need help creating a query

This is what I did, I used plpgsql,

create or replace function first_accum(anyelement, anyelement) returns
anyelement as $$
BEGIN
IF $1 IS NOT NULL THEN return $1;
ELSE return $2;
END IF;
END' language plpgsql;

then I created the aggregate
CREATE AGGREGATE first(sfunc = first_accum, basetype = anyelement, stype =
anyelement);

first_accum is basically the same thing as coalesce, but CREATE AGGREGATE
wasn't allowing me to use coalesce.

now I can get the salaries and positions each worker had on a given date.

SELECT name, first(startdate), first(salary)
FROM worker
JOIN position ON position.worker_id=worker.worker_id
WHERE fecha<='2006-05-01'
ORDER BY fecha DESC;

I'd appreciate some feedback, I hope there's a better way to do this. (maybe
without creating the plpgsql function but using an internal function)

On 7/14/06, Sergio Duran <sergioduran(at)gmail(dot)com> wrote:

> Nice, Richard, but you use max(startdate), how about the salary? i cant
> use max(salary) how about if he got a pay cut?
>
> My current solution is to write the nested query on the field list, like
> SELECT worker.*,
> (select salary
> FROM position where worker_id=worker.worker_id
> and fecha<='2006-04-01' LIMIT 1) as salary
> FROM worker;
>
> but I can only return 1 column from that subquery and repeating the same
> subquery for each column needed (position, date and salary) seems a little
> too much, if I write a procedure would postgres would optimize the access?
>
>
>
> On 7/13/06, Richard Broersma Jr <rabroersma(at)yahoo(dot)com> wrote:
> >
> > >
> > > worker: worker_id, name
> > > position: position_id, worker_id, position, startdate, salary
> > >
> > > If I perfom a query joining both tables, I can obtain all the workers
> > and
> > > the positions the've had.
> > >
> > > SELECT name, startdate, position, salary FROM worker JOIN position
> > > USING(worker_id);
> > > worker1 | 2001-01-01 | boss | 999999
> > > worker2 | 2001-01-01 | cleaning | 100
> > > worker2 | 2006-04-01 | programmer | 20000
> > > worker2 | 2006-07-04 | management | 25000
> > >
> > > so far so good, now I need to obtain all the workers only with the
> > position
> > > they had on a given date.
> > > if I wanted to know the positions on '2006-05-01' it would return
> > > worker1 | 2001-01-01 | boss | 999999
> > > worker2 | 2006-04-01 | programmer | 20000
> > >
> >
> > This is just a quick guess. I am not sure if the logic is correct but it
> > could be a starting
> > point.
> >
> > select P2.worker_id, P2.pdate, P1.position, P1.salary
> > from position as P1
> > join
> > (select worker_id, max(startdate) as pdate
> > from position
> > where startdate <= '2006-05-01'
> > group by worker_id, position_id) as P2
> > on (P1.worker_id = P2.worker_id) and (P1.startdate = P2.pdate)
> > ;
> >
> > Regards,
> >
> > Richard Broersma Jr.
> >
>
>