Check out example codes for "postgresql user permissions to database". It will help you in understanding the concepts better.

Code Example 1

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

Code Example 2

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

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