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+---
+title: PSQl Cheat Sheet
+template: post
+subtitle: Basic Commands
+excerpt: Login to postgresql
+date: 2022-04-04T17:27:00.746Z
+image: /blog/psql.jpg
+thumb_image: /blog/psql-schema.jpg
+image_position: right
+author: src/data/authors/bgoon.yaml
+show_author_bio: true
+cmseditable: true
+---
+# 🧘♂ PSQL
+
+> source
+
+## 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
+
+### Determine system tables
+
+```
+select * from pg_tables where tableowner = 'postgres';
+```
+
+### List databases from within a pg shell
+
+### List databases from UNIX command prompt
+
+### Describe a table
+
+### Quit psql
+
+### Switch postgres database within admin login shell
+
+### Reset a user password as admin
+
+```
+alter user usertochange with password 'new_passwd';
+```
+
+### Show all tables
+
+### List all Schemas
+
+### List all users
+
+### 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
+
+### 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 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](https://gist.github.com/kagemusha/1569836)
+
+### 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:
+
+* [PostgreSQL 9.6.0 Documentation](https://www.postgresql.org/docs/9.6/static/app-psql.html)
+* [PostgreSQL Exercises](https://pgexercises.com)
+* [PostgreSQL Tutorial](http://www.postgresqltutorial.com/postgresql-cheat-sheets)