create type time_interval as (
  start timestamp,
  stop timestamp
);
-- + ешё 9kb исходников

create table test1 ( 
	id int4,
	period time_interval,
	value varchar
);
create unique index uix on test1 (id, period time_interval_ops );
create index ix on test1( id, ( (period).start ) );
create index ix1 on test1( ( (period).start ) );

insert into test1( id, period, value )
select i, (now - (j)*'1 day'::interval, now - (j- 1 )*'1 day'::interval)::time_interval,
    'value '||i||' '||j
from generate_series(  1 ,  500  ) as i, generate_series(  1 ,  400  ) as j,
     ( select date_trunc('day', now()) as now ) as t;

select * from test1 where id =  333  and period = now()::timestamp-'10 week'::interval;
id; period; value
--------------------------------------------------------
 333 ;"(" 2008 - 09 - 15   00 : 00 : 00 "," 2008 - 09 - 16   00 : 00 : 00 ")";"value 333 70"

explain analyze select * from test1 where id =  333  and period = now()::timestamp-'10 week'::interval;
---------------------------------------------------
"Index Scan using uix on test1  (cost=0.26..338.95 rows=196 width=49) (actual time=0.402..0.407 rows=1 loops=1)"
"  Index Cond: ((id = 333) AND (period = ((now())::timestamp without time zone - '70 days'::interval)))"
"Total runtime: 0.492 ms"

explain analyze select * from test1 where id =  333  and
	    (period).start <= now()::timestamp-'10 week'::interval 
	and (period).stop > now()::timestamp-'10 week'::interval;
----------------------------------------------------
"Index Scan using ix on test1  (cost=0.01..233.28 rows=44 width=49) (actual time=0.933..0.935 rows=1 loops=1)"
"  Index Cond: ((id = 333) AND ((period).start <= ((now())::timestamp without time zone - '70 days'::interval)))"
"  Filter: ((period).stop > ((now())::timestamp without time zone - '70 days'::interval))"
"Total runtime: 0.886 ms"

insert into test1( id, period, value )
select  333 , (now() - '11 day'::interval, now() - '10 day'::interval)::time_interval,
    'value '|| 333 ||' '|| 10 ;
----------------------------------------------------
ERROR:  duplicate key value violates unique constraint "uix"

********** Ошибка **********

ERROR: duplicate key value violates unique constraint "uix"
SQL state:  23505 

explain analyze select * from test1 where period = now()::timestamp-'10 week'::interval;
---------------------------------------------------------------------------------------
"Index Scan using uix on test1  (cost=0.26..16802.73 rows=100000 width=49) (actual time=1.637..789.308 rows=500 loops=1)"
"  Index Cond: (period = ((now())::timestamp without time zone - '70 days'::interval))"
"Total runtime: 789.974 ms"

explain analyze select * from test1 where
	    (period).start <= now()::timestamp-'10 week'::interval 
	and (period).stop > now()::timestamp-'10 week'::interval;
---------------------------------------------------------------------------------------
"Bitmap Heap Scan on test1  (cost=1241.84..5303.85 rows=22222 width=49) (actual time=115.540..458.447 rows=500 loops=1)"
"  Recheck Cond: ((period).start <= ((now())::timestamp without time zone - '70 days'::interval))"
"  Filter: ((period).stop > ((now())::timestamp without time zone - '70 days'::interval))"
"  ->  Bitmap Index Scan on ix1  (cost=0.00..1236.28 rows=66667 width=0) (actual time=114.911..114.911 rows=165500 loops=1)"
"        Index Cond: ((period).start <= ((now())::timestamp without time zone - '70 days'::interval))"
"Total runtime: 459.885 ms"