Cheatsheets

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Postgresql

Basic Commands

Login to postgresql

psql -U postgres
psql -d mydb -U myuser -W
psql -h myhost -d mydb -U myuser -W
psql -U myuser -h myhost "dbname=mydb sslmode=require" # ssl connection

Default Admin Login

sudo -u postgres psql -U postgres
sudo -u postgres psql

List databases on postgresql server

psql -l [-U myuser] [-W]

Turn off line pager pagination in psql:

\pset pager

Determine system tables

select * from pg_tables where tableowner = 'postgres';

List databases from within a pg shell

\l

List databases from UNIX command prompt

psql -U postgres -l

Describe a table

\d tablename

Quit psql

\q

Switch postgres database within admin login shell

\connect databasename

Reset a user password as admin

alter user usertochange with password 'new_passwd';

Show all tables

\dt

List all Schemas

\dn

List all users

\du

Load data into postgresql

psql -W -U username -H hostname < file.sql

Dump (Backup) Data into file

pg_dump -W -U username -h hostname database_name > file.sql

Increment a sequence

SELECT nextval('my_id_seq');

Create new user

CREATE USER lemmy WITH PASSWORD 'myPassword';
# or

sudo -u postgres createuser lemmy -W

Change user password

ALTER USER Postgres WITH PASSWORD 'mypass';

Grant user createdb privilege

ALTER USER myuser WITH createdb;

Create a superuser user

create user mysuper with password '1234' SUPERUSER
# or even better
create user mysuper with password '1234' SUPERUSER CREATEDB CREATEROLE INHERIT LOGIN REPLICATION;
# or
sudo -u postgres createuser lemmy -W -s

Upgrade an existing user to superuser

alter user mysuper with superuser;
# or even better
alter user mysuper with SUPERUSER CREATEDB CREATEROLE INHERIT LOGIN REPLICATION

Show Database Version

SELECT version();

Change Database Owner

alter database database_name owner to new_owner;

Copy a database

CREATE DATABASE newdb WITH TEMPLATE originaldb;

View Database Connections

SELECT * FROM pg_stat_activity;

View show data directory (works on 9.1+)

show data_directory;

Show run-time parameters

show all;
select * from pg_settings;

Show the block size setting

# show block_size;
 block_size
------------
 8192
(1 row)

Show stored procedure source

SELECT prosrc FROM pg_proc WHERE proname = 'procname'

Grant examples

# readonly to all tables for myuser
grant select on all tables in schema public to myuser;
# all privileges on table1 and table2 to myuser
grant all privileges on table1, table2, table3 to myuser;

Restore Postgres .dump file

pg_restore --verbose --clean --no-acl --no-owner -h localhost -U myuser -d mydb latest.dump

source

Find all active sessions and kill them (i.e. for when needing to drop or rename db)

Source: http://stackoverflow.com/questions/5408156/how-to-drop-a-postgresql-database-if-there-are-active-connections-to-it

# Postgres 9.6 and above
SELECT pg_terminate_backend(pg_stat_activity.pid)
FROM pg_stat_activity
WHERE pg_stat_activity.datname = 'TARGET_DB'
 AND pid <> pg_backend_pid();

# Postgres 9.6 and below
SELECT pg_terminate_backend(pg_stat_activity.procpid)
FROM pg_stat_activity
WHERE pg_stat_activity.datname = 'TARGET_DB'
AND procpid <> pg_backend_pid();

Handy Queries

-- List procedure/function
SELECT * FROM pg_proc WHERE proname='__procedurename__';

-- List view (including the definition)
SELECT * FROM pg_views WHERE viewname='__viewname__';

-- Show DB table space in use
SELECT pg_size_pretty(pg_total_relation_size('__table_name__'));:

-- Show DB space in use
SELECT pg_size_pretty(pg_database_size('__database_name__'));

-- Show current user's statement timeout
show statement_timeout;

-- Show table indexes
SELECT * FROM pg_indexes WHERE tablename='__table_name__' AND schemaname='__schema_name__';

-- Get all indexes from all tables of a schema:
SELECT
   t.relname AS table_name,
   i.relname AS index_name,
   a.attname AS column_name
FROM
   pg_class t,
   pg_class i,
   pg_index ix,
   pg_attribute a,
   pg_namespace n
WHERE
   t.oid = ix.indrelid
   AND i.oid = ix.indexrelid
   AND a.attrelid = t.oid
   AND a.attnum = ANY(ix.indkey)
   AND t.relnamespace = n.oid
   AND n.nspname = 'kartones'
ORDER BY
   t.relname,
   i.relname

-- Queries being executed at a certain DB
SELECT datname, application_name, pid, backend_start, query_start, state_change, state, query
  FROM pg_stat_activity
  WHERE datname='__database_name__';

-- Get all queries from all dbs waiting for data (might be hung)
SELECT * FROM pg_stat_activity WHERE waiting='t';

Query analysis

-- See the query plan for the given query
EXPLAIN __query__

-- See and execute the query plan for the given query
EXPLAIN ANALYZE __query__

-- Collect statistics
ANALYZE [__table__]

Querying Data

From a Single Table

-- Query data in columns c1, c2 from a table
SELECT c1, c2 FROM t;

-- Query distinct rows from a table
SELECT DISTINCT c1
FROM t
WHERE condition;

-- Sort the result set in ascending or descending order
SELECT c1, c2
FROM t
ORDER BY c1 ASC [DESC];

-- Skip offset of rows and return the next n rows
SELECT c1, c2
FROM t
ORDER BY c1
LIMIT n
OFFSET offset;

-- Group rows using an aggregate function
SELECT c1, aggregate(c2)
FROM t
GROUP BY c1;

-- Filter groups using HAVING clause
SELECT c1, aggregate(c2) FROM t
GROUP BY c1
HAVING condition;

From Multiple Tables

-- Inner join t1 and t2
SELECT c1, c2
FROM t1
INNER JOIN t2
ON condition;

-- Left join t1 and t1
SELECT c1, c2
FROM t1
LEFT JOIN t2
ON condition;

-- Right join t1 and t2
SELECT c1, c2
FROM t1
RIGHT JOIN t2
ON condition;

-- Perform full outer join
SELECT c1, c2
FROM t1
FULL OUTER JOIN t2
ON condition;

-- Produce a Cartesian product of rows in tables
SELECT c1, c2
FROM t1
CROSS JOIN t2;

-- Another way to perform cross join
SELECT c1, c2
FROM t1, t2;

-- Join t1 to itself using INNER JOIN clause
SELECT c1, c2
FROM t1 A
INNER JOIN t2 B ON condition

Using SQL Operators

-- Combine rows from two queries
SELECT c1, c2 FROM t1
UNION [ALL]
SELECT c1, c2 FROM t2;

-- Return the intersection of two queries
SELECT c1, c2 FROM t1
INTERSECT
SELECT c1, c2 FROM t2;

-- Subtract a result set from another result set
SELECT c1, c2 FROM t1
EXCEPT
SELECT c1, c2 FROM t2;

-- Query rows using pattern matching %, _
SELECT c1, c2 FROM t1
WHERE c1 [NOT] LIKE pattern;

-- Query rows in a list
SELECT c1, c2
FROM t
WHERE c1
[NOT] IN value_list;

-- Query rows between two values
SELECT c1, c2
FROM t
WHERE c1
BETWEEN low AND high;

-- Check if values in a table is NULL or not
SELECT c1, c2 FROM t
WHERE c1 IS [NOT] NULL;

Source: