In this blog I have listed some of the basic commands like installing PostgreSQL, creating user and databases for PostgreSQL etc. CRUD with PostgreSQL is not the focus of this post. All the commands are tested in Ubuntu 14.04 LTS and Ubuntu 16.04 LTS. There may be some other richer ways to perform the operations mentioned in this post but my focus was to keep the stuff simple with minimal complexity. I have used the terms ‘user’ and ‘role’ interchangeably in the blog, as they are analogous with respect to PostgreSQL.
1) Install PostgreSQL
sudo apt-get update sudo apt-get install postgresql -y
2) Check PostgreSQL version.
3) Login to PostgreSQL
Login as default user ie ‘postgres’ with password as ‘password_of_your_ubuntu_system’
sudo -u postgres psql
4) Create a new user for PostgreSQL and assign a password to it
Since it is not considered a good practice to persist your data in PostgreSQL through the default user ie ‘postgres’, we will create a new user and assign a password to it. It can be done by 2 possible ways as follows ->
First Way :
sudo -u postgres createuser --interactive
Here, you would be asked name of the role/user, if you want to assign superuser privileges to the new user or not; and if not whether the user be allowed to create databases and new roles.
After creating the user, login to PostgreSQL console via the default user ie ‘postgres’ and then alter the password for the user via following command (Assuming the new user/role you created is lihas) :
ALTER USER lihas WITH PASSWORD 'lihas';
In case the name of your user contains capital letters, wrap the user name into double qoutes while performing all user related operations like :
ALTER USER "LiHaS" WITH PASSWORD 'lihas';
Second Way :
Login to PostgreSQL console via the default user ie ‘postgres’ and then create the user :
CREATE USER lihas WITH PASSWORD 'lihas'; --Assuming the new user/role we want to create is lihas ALTER USER lihas WITH CREATEDB; --user lihas con create databases ALTER USER lihas WITH CREATEUSER; --user lihas con create new users/roles
5) List all users in PostgreSQL
6) Switch to a user
SET ROLE user_name;
7) Check current user
8) Delete a user/role
DROP USER user_name;
9) List all databases
10) Creating Database
CREATE DATABASE lihas_db;
By default owner of the any database you create is ‘postgres’, if you want your database to belong to a specific user, switch to that user (see command 6 above) and then create the database.
11) Enter inside a database
Enter inside database via the default user
Enter inside database with a specific user
\c database_name user_name
If the above command does not work (Peer authentication failed), simply change the database first and then switch to the user (see command 6 above).
You may also login directly into a database with a certain user from the terminal by following command (with password as ‘password_of_your_ubuntu_system’ )
sudo -u role_name psql db_name
But for this command to work, role_name must be a valid Linux user name. You may add a user to Linux by following :
sudo adduser role_name;
12) Dropping database
DROP DATABASE db_name;
13) List all tables
14) Describe schema of a table
15) Exit out of PostgreSQL
Hope this compilation helps you. Share your thoughts in the comments below.