psql and the catalog

What you will be able to do

• Connect with psql using host port 15432
• List tables and describe a table with \dt and \d
• Run a one-shot query with psql -c

Why this matters for data work

Before writing a clever query, you look at what exists. psql meta-commands (\d, \dt) are the warehouse equivalent of ls and cat on schemas.

Concepts

Command	Meaning
\dt	list tables
\d orders	describe columns and keys
\x	toggle expanded display
\q	quit
-c "SQL"	one shot from the shell

Practice on your machine

export PGPASSWORD=dcubes PGHOST=127.0.0.1 PGPORT=15432 PGUSER=dcubes PGDATABASE=retail
psql

Inside psql:

\dt
\d orders
\d stores
SELECT store_id, store_name FROM stores ORDER BY store_id;
\q

One-shot:

psql -c "\dt"
psql -c "SELECT category, count(*) FROM products GROUP BY 1 ORDER BY 1;"

What you should see

• Three tables: orders, products, stores.
• orders columns matching the CSV header.
• Five stores when you SELECT.

Common mistakes

• Forgetting PGPASSWORD — psql prompts or fails.
• Wrong database — \c retail if you landed elsewhere.
• Typing SQL meta as SQL — \dt is not SELECT \dt.

Next

SELECT and WHERE