psql is PostgreSQL's interactive command-line client — used to connect to a database and run queries, inspect the schema, and administer the database. It has special meta-commands (starting with \) for navigation and administration, beyond running SQL.
psql -U username -d database_name -h host -p 5432
psql postgresql://user:pass@host:5432/dbname
psql mydb
\l list all databases
\c dbname connect to a database
\dt list TABLES in the current database
\d tablename describe a table (columns, types, indexes, constraints)
\di list indexes
\dn list schemas
\du list roles/users
\df list functions
\dv list views
\x toggle expanded display (vertical — readable for wide rows)
\timing toggle query timing
\? help on meta-commands
\h SELECT help on a SQL command
\q quit
These \ meta-commands let you explore and administer the database quickly — \dt (list tables), \d tablename (inspect a table's structure), and \l (list databases) are used constantly.
SELECT * FROM users LIMIT 5; -- run SQL directly (end with ;)
psql -d mydb -f script.sql -- run a SQL FILE
psql -d mydb -c "SELECT count(*) FROM users" -- run a single command and exit
\i script.sql -- run a file from within psql
\copy users TO 'users.csv' CSV HEADER -- export to CSV (client-side)
\x auto auto-switch to vertical display for wide results
\timing on show how long each query takes
\e open the last query in an editor
\set, \pset configure variables and output formatting
psql is the essential, everyday tool for working directly with PostgreSQL — developers and DBAs use it constantly to connect, query, inspect, and administer databases, so knowing its essentials is practical, fundamental knowledge for Postgres work.
While GUI tools exist, psql is the universal, always-available interface (present wherever Postgres is), and its meta-commands (\) make it especially powerful for quick database exploration and administration that pure SQL can't do conveniently: \dt (list tables), \d tablename (inspect a table's full structure — columns, types, indexes, constraints — a constant need), \l (list databases), \du (list users/roles), and others let you navigate and understand a database rapidly.
Knowing how to connect (with options or a URL), run queries and scripts (-f for files, -c for one-off commands), use the meta-commands for inspection, and helpful settings (\x for readable wide-row display, \timing for query timing) is everyday practical knowledge for any Postgres developer or administrator.
Since psql is the standard, ubiquitous command-line interface to PostgreSQL — used for development, debugging, administration, scripting, and exploration — understanding its essential commands and workflow is valuable, frequently-applied knowledge that makes working with Postgres efficient, and it's a basic competency expected of anyone working with the database directly.