07. Hello PostgreSQL

The psql command-line tool is really powerful. There's a complete reference to it in the PostgreSQL documentation.

To connect psql to a database running on the same machine (such as your VM), all you need to give it is the database name. For instance, the command psql forum will connect to the forum database.

From within psql, you can run any SQL statement using the tables in the connected database. Make sure to end SQL statements with a semicolon, which is not always required from Python.

You can also use a number of special psql commands to get information about the database and make configuration changes. The \d posts command shown in the video is one example — this displays the columns of the posts table.

Some other things you can do:

\dt — list all the tables in the database.

\dt+ — list tables plus additional information (notably, how big each table is on disk).

\H — switch between printing tables in plain text vs. HTML.

Here's a fun one to run in psql while your forum web app is running:

select * from posts \watch

(Note that \watch replaces the semicolon.) This will display the contents of the posts table and refresh it every two seconds, so you can see changes to the table as you use the app.

In order to do this, you'll need two terminal sessions into your VM — one running the forum app, and the other running psql. You can connect to the VM from any number of terminal windows at once — just open up another terminal, change to the vagrant directory, and type vagrant ssh again.