currval of sequence "follow_id_seq" is not yet defined in this session

postgresql上使用

1. select currval('follow_id_seq');

报错：

1. currval of sequence "follow_id_seq" is not yet defined in this session

查阅参考资料，发现错误原因是要查当前值，必须先取一次next：执行以下语句，执行成功：

1. dbname=# select nextval('follow_id_seq');
2. nextval
3. ---------
4. 5347
5. (1 row)
6. dbname=# select currval('follow_id_seq');
7. currval
8. ---------
9. 5347
10. (1 row)

http://sunboyyyl.blog.163.com/blog/static/224738120099135521859/