Basic commands:
psql -U <username> # connect to DB
\l -- list DBs
\dt -- list tables
\d <table> -- table details
\du[+] -- list users and roles
\x -- expanded display
show data_directory -- where DB files are stored
show all -- run-time configuration of DB
SELECT * FROM <table>;
SELECT
last_name,
first_name
FROM
customer
WHERE
first_name = 'Jamie'
AND last_name = 'Rice';
-- % -> .*, _ -> .
SELECT * FROM customer WHERE last_name LIKE '%gen%';
-- NOTE: you should do corresponding SELECT before doing UPDATE
UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';