PostgreSQL

Getting Started

Getting started

Switch and connect

$ sudo -u postgres psql

List all databases

postgres=# \l

Connect to the database named postgres

postgres=# \c postgres

Disconnect

postgres=# \q
postgres=# \!

psql commands

Getting help

Run in PostgreSQL console

PostgreSQL Working

Recon

Show version

SHOW SERVER_VERSION;

Show system status

\conninfo

Show environmental variables

SHOW ALL;

List users

SELECT rolname FROM pg_roles;

Show current user

SELECT current_user;

Show current user’s permissions

\du

Show current database

SELECT current_database();

Show all tables in database

\dt

List functions

\df <schema>

Databases

List databases

\l

Connect to database

\c <database_name>

Show current database

SELECT current_database();

Create database

CREATE DATABASE <database_name> WITH OWNER <username>;

Drop database

DROP DATABASE IF EXISTS <database_name>;

Rename database

ALTER DATABASE <old_name> RENAME TO <new_name>;

Tables

List tables, in current db

\dt

SELECT table_schema,table_name FROM information_schema.tables ORDER BY table_schema,table_name;

List tables, globally

\dt *.*.

SELECT * FROM pg_catalog.pg_tables

List table schema

\d <table_name>
\d+ <table_name>

SELECT column_name, data_type, character_maximum_length
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = '<table_name>';

Create table

CREATE TABLE <table_name>(
  <column_name> <column_type>,
  <column_name> <column_type>
);

Create table, with an auto-incrementing primary key

CREATE TABLE <table_name> (
  <column_name> SERIAL PRIMARY KEY
);

Delete table

DROP TABLE IF EXISTS <table_name> CASCADE;

Permissions

Become the postgres user, if you have permission errors

sudo su - postgres
psql

Grant all permissions on database

GRANT ALL PRIVILEGES ON DATABASE <db_name> TO <user_name>;

Grant connection permissions on database

GRANT CONNECT ON DATABASE <db_name> TO <user_name>;

Grant permissions on schema

GRANT USAGE ON SCHEMA public TO <user_name>;

Grant permissions to functions

GRANT EXECUTE ON ALL FUNCTIONS IN SCHEMA public TO <user_name>;

Grant permissions to select, update, insert, delete, on a all tables

GRANT SELECT, UPDATE, INSERT ON ALL TABLES IN SCHEMA public TO <user_name>;

Grant permissions, on a table

GRANT SELECT, UPDATE, INSERT ON <table_name> TO <user_name>;

Grant permissions, to select, on a table

GRANT SELECT ON ALL TABLES IN SCHEMA public TO <user_name>;

Columns

Add column

ALTER TABLE <table_name> IF EXISTS
ADD <column_name> <data_type> [<constraints>];

Update column

ALTER TABLE <table_name> IF EXISTS
ALTER <column_name> TYPE <data_type> [<constraints>];

Delete column

ALTER TABLE <table_name> IF EXISTS
DROP <column_name>;

Update column to be an auto-incrementing primary key

ALTER TABLE <table_name>
ADD COLUMN <column_name> SERIAL PRIMARY KEY;

Insert into a table, with an auto-incrementing primary key

INSERT INTO <table_name>
VALUES (DEFAULT, <value1>);


INSERT INTO <table_name> (<column1_name>,<column2_name>)
VALUES ( <value1>,<value2> );

Data

Select all data

SELECT * FROM <table_name>;

Read one row of data

SELECT * FROM <table_name> LIMIT 1;

Search for data

SELECT * FROM <table_name> WHERE <column_name> = <value>;

Insert data

INSERT INTO <table_name> VALUES( <value_1>, <value_2> );

Update data

UPDATE <table_name>
SET <column_1> = <value_1>, <column_2> = <value_2>
WHERE <column_1> = <value>;

Delete all data

DELETE FROM <table_name>;

Delete specific data

DELETE FROM <table_name>
WHERE <column_name> = <value>;

Users

List roles

SELECT rolname FROM pg_roles;

Create user

CREATE USER <user_name> WITH PASSWORD '<password>';

Drop user

DROP USER IF EXISTS <user_name>;

Alter user password

ALTER ROLE <user_name> WITH PASSWORD '<password>';

Schema

List schemas

\dn

SELECT schema_name FROM information_schema.schemata;

SELECT nspname FROM pg_catalog.pg_namespace;

Create schema

CREATE SCHEMA IF NOT EXISTS <schema_name>;

Drop schema

DROP SCHEMA IF EXISTS <schema_name> CASCADE;

Dates

Show current date YYYY-MM-DD

SELECT current_date;

Calculate age between two dates

SELECT age(timestamp, timestamp);

Show current time with time zone

SELECT current_time;

Make dates using integers

SELECT make_date(2021,03,25);

PostgreSQL Commands

Tables

Query buffer

Informational

S: show system objects, +: additional detail

Connection

Formatting

Input/Output

Variables

Misc

Large Objects

• \lo_export LOBOID FILE
• \lo_import FILE [COMMENT]
• \lo_list
• \lo_unlink LOBOID

Miscellaneous

Backup

Use pg_dumpall to backup all databases

$ pg_dumpall -U postgres > all.sql

Use pg_dump to backup a database

$ pg_dump -d mydb -f mydb_backup.sql

•   -a   Dump only the data, not the schema
•   -s   Dump only the schema, no data
•   -c   Drop database before recreating
•   -C   Create database before restoring
•   -t   Dump the named table(s) only
•   -F   Format (c: custom, d: directory, t: tar) {.marker-none}

Use pg_dump -? to get the full list of options

Restore

Restore a database with psql

$ psql -U user mydb < mydb_backup.sql

Restore a database with pg_restore

$ pg_restore -d mydb mydb_backup.sql -c

•   -U   Specify a database user
•   -c   Drop database before recreating
•   -C   Create database before restoring
•   -e   Exit if an error has encountered
•   -F   Format (c: custom, d: directory, t: tar, p: plain text sql(default)) {.marker-none}

Use pg_restore -? to get the full list of options

Remote access

Get location of postgresql.conf

$ psql -U postgres -c 'SHOW config_file'

Append to postgresql.conf

listen_addresses = '*'

Append to pg_hba.conf (Same location as postgresql.conf)

host  all  all  0.0.0.0/0  md5
host  all  all  ::/0       md5

Restart PostgreSQL server

$ sudo systemctl restart postgresql

Import/Export CSV

Export table into CSV file

\copy table TO '<path>' CSV
\copy table(col1,col1) TO '<path>' CSV
\copy (SELECT...) TO '<path>' CSV

Import CSV file into table

\copy table FROM '<path>' CSV
\copy table(col1,col1) FROM '<path>' CSV

See also: Copy

Also see

• Posgres-cheatsheet (gist.github.com)

• MongoDB
• MongoDB
• Neo4j
• Neo4j
• PostgreSQL