psql (8.4devel)
You are now connected to database "prueba".

create database prueba;
\c prueba
create table tabname (anio integer, mes integer);
explain analyze select * from tabname;
                                             QUERY PLAN

-----------------------------------------------------------------------------------------------------
 Seq Scan on tabname  (cost=0.00..31.40 rows=2140 width=8) (actual time=0.003..0.003 rows=0 loops=1)
 Total runtime: 0.066 ms
(2 rows)

analyze;
explain analyze select * from tabname;
                                             QUERY PLAN

-----------------------------------------------------------------------------------------------------
 Seq Scan on tabname  (cost=0.00..31.40 rows=2140 width=8) (actual time=0.003..0.003 rows=0 loops=1)
 Total runtime: 0.050 ms
(2 rows)

insert into tabname values (1, 1);
analyze;
explain analyze select * from tabname;
                                           QUERY PLAN

-------------------------------------------------------------------------------------------------
 Seq Scan on tabname  (cost=0.00..1.01 rows=1 width=8) (actual time=0.008..0.010 rows=1 loops=1)
 Total runtime: 0.057 ms
(2 rows)