-- lets play with sequences:
create table items (id serial primary key, name varchar(10));
insert into items(name) values ('foo');
-- manually insert into a serial is allowed BUT it breaks the sequence!
insert into items(id,name) values (2,'foo');
-- now what do you expect?
select currval(pg_get_serial_sequence('items', 'id')); -- ouch! nextval is 1!!
-- ok, let's fix it up!
SELECT setval(pg_get_serial_sequence('items', 'id'), (select max(id)+1 from public.items));