postgres=# create role test with login;
CREATE ROLE
postgres=# grant all on database postgres to test;
GRANT
postgres=# drop role test;
ERROR: role "test" cannot be dropped because some objects depend on it
DETAIL: privileges for database postgres

postgres=# revoke all on database postgres from test;
REVOKE
postgres=# drop role test;
DROP ROLE

postgres=# create role test with login;
CREATE ROLE
postgres=# \c - test
You are now connected to database "postgres" as user "test".
postgres=> create table test (id int);
CREATE TABLE
postgres=# \c - postgres
You are now connected to database "postgres" as user "postgres".
postgres=# drop role test;
ERROR: role "test" cannot be dropped because some objects depend on it
DETAIL: owner of table test

postgres=# alter table test OWNER TO postgres;
ALTER TABLE
postgres=# drop role test;
DROP ROLE

postgres=# REASSIGN OWNED BY test TO postgres;
REASSIGN OWNED
postgres=# DROP OWNED BY test;
DROP OWNED
postgres=# drop role test;
DROP ROLE

postgres=# REASSIGN OWNED BY test TO postgres;
REASSIGN OWNED
postgres=# drop role test;
DROP ROLE

sudo su - postgres #切换到postgres用户(系统用户)
createdb weichen #创建数据库
psql #直接访问数据库(默认进入本地postgres数据库)
\l --查看数据库列表
:q --退出列表页面
\q --退出客户端
dropdb weichen #删除数据库

sudo -u postgres psql #登录客户端
create database weichen; --创建数据库
create database sz owner postgres; --创建数据库
select oid,datname from pg_database; --查看数据库列表
drop database weichen; --删除数据库
drop database sz; --删除数据库