Andreas Kretschmer <akretschmer@spamfence.net> schrieb:
> Jonathan Davies <jonathan@nixondesign.com> schrieb:
>
> >
> > Hi
> > I have a car parking reservation table that stores 2 timestamps entry_date and
> > exit_date.
> > There is a maximum number of car parking places, and I want to check that on
> > each day between the 2 requested reservation dates, the count of the existing
> > records does not exceed the maximum.
Btw.:
you can create a trigger like this:
(with a fixed limit of 6 places)
create or replace function check_parking() returns trigger as $$
declare counter int;
begin
select into counter max(x.sum) from (select (NEW.entry + (g.n||'days')::interval)::date,
sum(case when (NEW.entry + (g.n||'days')::interval)::date between a.entry and a.exit then 1 else 0 end)
from parking a, generate_series(0,NEW.exit-NEW.entry) g(n) group by g.n order by 1) as x;
if counter > 5 then -- limit -1!!!
raise exception 'not possible';
else
return NEW;
end if;
end;
$$ language plpgsql;
create trigger parking_check before insert or update on parking for each row execute procedure check_parking();
Now a test:
test=# select * from parking ;
id | entry | exit
----+------------+------------
1 | 2006-03-01 | 2006-03-30
2 | 2006-03-15 | 2006-04-15
3 | 2006-03-30 | 2006-04-30
(3 rows)
test=# insert into parking values (4,'2006/03/02','2006/03/20');
INSERT 0 1
test=# insert into parking values (5,'2006/03/12','2006/03/20');
INSERT 0 1
test=# insert into parking values (5,'2006/03/10','2006/03/20');
INSERT 0 1
test=# insert into parking values (6,'2006/03/10','2006/03/20');
INSERT 0 1
test=# insert into parking values (7,'2006/03/10','2006/03/20');
ERROR: not possible
HTH, Andreas
--
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unintentional side effect. (Linus Torvalds)
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