give access to partivular db psql code example

Example 1: psql set access privileges

REVOKE ALL ON DATABASE example_database FROM example_user;
GRANT CONNECT ON DATABASE example_database TO example_user;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO example_user;

Example 2: postgresql user permissions to database

sudo -u postgres 
psqlpostgres=# create database mydb;
postgres=# create user myuser with encrypted password 'mypass';
postgres=# grant all privileges on database mydb to myuser;