drop table tttest;

create table tttest (
	price_id	int4, 
	price_val	int4, 
	price_on	abstime,
	price_off	abstime
);

create trigger timetravel 
	before insert or delete or update on tttest
	for each row 
	execute procedure 
	timetravel (price_on, price_off);

insert into tttest values (1, 1, null, null);
insert into tttest(price_id, price_val) values (2, 2);
insert into tttest(price_id, price_val,price_off) values (3, 3, 'infinity');

insert into tttest(price_id, price_val,price_off) values (3, 3, 
	abstime('now'::timestamp - '100 days'::interval));
insert into tttest(price_id, price_val,price_on) values (3, 3, 'infinity');

select * from tttest;
delete from tttest where price_id = 2;
select * from tttest;
-- what do we see ?

-- get current prices
select * from tttest where price_off = 'infinity';

-- change price for price_id == 3
update tttest set price_val = 30 where price_id = 3;
select * from tttest;

-- now we want to change price_id from 3 to 5 in ALL tuples
-- but this gets us not what we need
update tttest set price_id = 5 where price_id = 3;
select * from tttest;

-- restore data as before last update:
select set_timetravel('tttest', 0);	-- turn TT OFF!
delete from tttest where price_id = 5;
update tttest set price_off = 'infinity' where price_val = 30;
select * from tttest;

-- and try change price_id now!
update tttest set price_id = 5 where price_id = 3;
select * from tttest;
-- isn't it what we need ?

select set_timetravel('tttest', 1);	-- turn TT ON!

-- we want to correct some date
update tttest set price_on = 'Jan-01-1990 00:00:01' where price_id = 5 and 
	price_off <> 'infinity';
-- but this doesn't work

-- try in this way
select set_timetravel('tttest', 0);	-- turn TT OFF!
update tttest set price_on = '01-Jan-1990 00:00:01' where price_id = 5 and 
	price_off <> 'infinity';
select * from tttest;
-- isn't it what we need ?

-- get price for price_id == 5 as it was '10-Jan-1990'
select * from tttest where price_id = 5 and 
	price_on <= '10-Jan-1990' and price_off > '10-Jan-1990';
