Re: How to write a constraint which need to check other table?

[纪晓曦 <sheepjxx@xxxxxxxxx>]

Thank you very much, I think I need to stady more about trigger.

2009/9/28 A. Kretschmer <andreas.kretschmer@xxxxxxxxxxxxxx>

In response to ????????? :

> Yes, you are right. That maybe a bad example. what I want to say maybe like
> this:
>
> create table a (
>          id integer,
>          room varchar(32),
>          start time,
>          end time,
>          PRIMARY KEY(id)
> )
> How can I check if it is the same room, when I insert the data, the start time
> and end time doesn't overlap?

Please answer to the list, okay?

test=*# create table a ( id int primary key, room char(32), start_time timestamp, end_time timestamp);
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "a_pkey" for table "a"
CREATE TABLE
test=*# create or replace function check_overlapp() returns trigger as $$begin perform id from a where room=new.room and (start_time,end_time) overlaps (new.start_time,new.end_time); if found then raise notice 'room reserved'; return null; else  return new; end if; end; $$language plpgsql;
CREATE FUNCTION
test=*# create trigger trg_check before insert or update on a for each row execute procedure check_overlapp();
CREATE TRIGGER
test=*# insert into a values (1, 'room1', '2009-10-01'::timestamptz, '2009-10-10'::timestamptz);
INSERT 0 1
test=*# insert into a values (2, 'room1', '2009-09-01'::timestamptz, '2009-09-10'::timestamptz);
INSERT 0 1
test=*# insert into a values (3, 'room1', '2009-09-08'::timestamptz, '2009-09-20'::timestamptz);
NOTICE:  room reserved
INSERT 0 0

You can also use RAISE EXCEPTION to force an error:

test=*# create or replace function check_overlapp() returns trigger as $$begin perform id from a where room=new.room and (start_time,end_time) overlaps (new.start_time,new.end_time); if found then raise exception 'room reserved'; return null; else  return new; end if; end; $$language plpgsql;
CREATE FUNCTION
test=*# insert into a values (3, 'room1', '2009-09-08'::timestamptz, '2009-09-20'::timestamptz);
ERROR:  room reserved
test=!#



HTH, Andreas

--
Andreas Kretschmer
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