Using psql

Using psql¶

Let us understand how to use psql utility to perform database operations.

• psql is command line utility to connect to the Postgres database server. It is typically used for the following by advanced Database users:
  • Manage Databases
  • Manage Tables
  • Load data into tables for testing purposes
• We need to have at least Postgres Client installed on the server from which you want to use psql to connect to Postgres Server.
• If you are on the server where Postgres Database Server is installed, psql will be automatically available.
• We can run sudo -u postgres psql -U postgres from the server provided you have sudo permissions on the server. Otherwise we need to go with psql -U postgres -W which will prompt for the password.
• postgres is the super user for the postgres server and hence typically developers will not have access to it in non development environments.
• As a developer, we can use following command to connect to a database setup on postgres server using user credentials.

psql  -h <host_ip_or_dns_alias> -d <db_name> -U <user_name> -W

# Here is the example to connect to itversity_sms_db using itversity_sms_user
psql -h localhost -p 5432 -d itversity_sms_db -U itversity_sms_user -W

• We typically use psql to troubleshoot the issues in non development servers. IDEs such as SQL Alchemy might be better for regular usage as part of development and unit testing process.
• For this course, we will be primarily using Jupyter based environment for practice.
• However, we will go through some of the important commands to get comfortable with psql.
  • Listing Databases – \l
  • Switching to a Database – \c <DATABASE_NAME>
  • Get help for psql – \?
  • Listing tables – \d
  • Create table – CREATE TABLE t (i SERIAL PRIMARY KEY)
  • Get details related to a table – \d <table_name>
  • Running Scripts – \i <SCRIPT_PATH>
  • You will go through some of the commands over a period of time.