postgresql如何让主键自增

1. 法一：
   
   Sql代码  收藏代码
   
   CREATE TABLE customers
   
   (
   
     customerid SERIAL primary key ,
   
     companyname character varying,
   
     contactname character varying,
   
     phone character varying,
   
     country character varying
   
   )
   
    法二：
   
   Sql代码  收藏代码
   
   CREATE SEQUENCE event_id_seq
   
   START WITH 1
   
   INCREMENT BY 1
   
   NO MINVALUE
   
   NO MAXVALUE
   
   CACHE 1;
   
   alter table event alter column id set default nextval('event_id_seq');