using the nextval('sequence_name') in sql, the result maybe is notright

Hi, all:

    PostgreSQL version : 10.3.  I use "nextval" in the sql , but I think the result is not right, maybe it is a bug.

   The test case as bellow:

   create sequence seq1;

select nextval('seq1');

create table tx1(id1 int, id2 int);

insert into tx1 select generate_series(1,100), random()*102;

explain verbose select * from tx1 where id2 = nextval('seq1');;

select * from tx1 where id2 = nextval('seq1');

postgres=# explain verbose select * from tx1 where id2 = nextval('seq1');; QUERY PLAN ------------------------------------------------------------ Seq Scan on public.tx1 (cost=0.00..43.90 rows=11 width=8) Output: id1, id2 Filter: (tx1.id2 = nextval('seq1'::regclass)) (3 rows)

Thanks,

    Wanglin