Useful PostgreSQL Commands#

PG example user

Many of these examples use a role (user) called devel.

Miscellaneous Commands#

Get PostgresSQL version:

SELECT version();

Get type of a value:

SELECT pg_typeof(1);
pg_typeof | integer

SELECT pg_typeof(1) as type_of_1;
type_of_1 | integer

SELECT pg_typeof(1::NUMERIC);
pg_typeof | numeric

blog1_dev=# SELECT pg_typeof('xyz');
pg_typeof | unknown

blog1_dev=# SELECT pg_typeof('xyz'::VARCHAR(8));
pg_typeof | character varying

blog1_dev=# SELECT pg_typeof('xyz'::TEXT);
pg_typeof | text

List pg types:

SELECT oid, typname, typlen FROM pg_type;

See:

Roles (users)#

Create role:

CREATE ROLE devel
WITH LOGIN PASSWORD 's3cr37' CREATEDB REPLICATION
VALID UNTIL 'infinity';

Creating Databases#

Create database:

CREATE DATABASE devel WITH
    ENCODING='UTF-8'
    OWNER=devel
    LC_CTYPE='en_US.UTF-8'
    LC_COLLATE='en_US.UTF-8'
    TEMPLATE=template0
    CONNECTION LIMIT=3;

Make role devel as powerful as postgres role:

ALTER USER devel WITH SUPERUSER;

Reverse the effects of the command above:

ALTER USER devel WITH NOSUPERUSER;

Backup & Restore#

Dump:

$ pg_dump -U devel -W mydb -f mydb.sql

Import:

psql -U devel -d mydb -f _stuff/mydb.sql

Restore a Heroku Postgres dump:

$ pg_restore -U devel -d mydb mydb.backup

Renaming a Database#

Make sure no user or application is connected to the database otherwise this command will not work:

devel=# ALTER DATABASE blog RENAME TO blog_dev;
ERROR:  database "blog" is being accessed by other users
DETAIL:  There is 1 other session using the database.

After no sessions are active, it should work:

devel=# ALTER DATABASE blog RENAME TO blog_dev;
ALTER DATABASE

Note the output is simply “ALTER DATABASE”, which means the command ran successfully.

References:

Tables#

PostgreSQL has \d and \dt to inspect a table. Those are not standard SQL, but PostgreSQL specific features. We can also use standard SQL to inspect a table (should work across many different database vendors):

SELECT 
    table_name
  , column_name 
  , data_type 
FROM 
   information_schema.columns
WHERE 
   table_name = 'users';

There is an overwhelming number of columns to display. See it for yourself:

SELECT *
FROM information_schema.columns
WHERE table_name = 'users';