1、序列

以自增serial类型主键的序列：

alter sequence s_seq restart with 1;　　#重置序列
select currval('tablename_pid_seq');
select nextval('tablename_pid_seq');
select setval('tablename_pid_seq',1);

2、修改表

--删除约束
alter table tablename alter column col drop not null;

--添加约束
alter table tablename add constraint tablename_col_uq unique(col);

--修改类型/长度
alter table tablename alter column col type character varying(2000);

--添加列
alter table tablename add column col character varying(255);

--删除列
alter table tablename drop column col; 

3、查看数据使用空间

select pg_size_pretty(pg_database_size('dbname'));