Postgresql Command Line Cheat Sheet

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  1. Introduction to the PostgreSQL cheat sheet Prerequisites to using PostgreSQL SQL commands in psql Accessing PostgreSQL using the ‘psql’ command line interface PostgreSQL cheat sheet of useful SQL queries and commands Use ‘SELECT’ to get a Postgres table’s column names PostgreSQL cheat sheet commands for modifying tables PostgreSQL cheat sheet for managing databases Use the a.
  2. Change database. Use c to change database names: mary= c marydb.
  3. You can do some of them through a visual user interface, but that's not covered here. Knowing how to perform these operations on the command line means you can script them, and scripting means you can automate tests, check errors, and do data entry on the command line. This section isn't a full cheat sheet for psql. It covers the most common operations and shows them roughly in sequence, as you'd use.

Introduction to the PostgreSQL cheat sheet

The PostgreSQL offers scaling, storage flexibility, and ease of database management for developers, DBAs, and other technical professionals. Because of PostgreSQL’s ability to offer architecture stability along with an extensive coding capability, the plethora of commands and statements are endless. That’s a good thing. What’s even better is having a handy list of the SQL commands you’re likely to use regularly. Well, some of the most popular ones are featured here in Part 2 of The PostgreSQL Cheat Sheet, so take a few moments to review it now.

Prerequisites to using PostgreSQL SQL commands in psql

  • Be sure that the object-relational database management systemPostgreSQL installed on your OS.

  • At the command line psql, check the PostgreSQL version with the command psql -V.

  • You’ll also need PostgreSQL database accessibility to try out the samples shown in this PostgreSQL cheat sheet.

NOTE: Here are some useful tips regarding commands. When writing code in psql, always end your SQL statement with a semicolon (;). If you don’t and push Return, your code will extend to the next line of code without breaking at the place where you wanted it to end.

Another tip for writing SQL statements is to remember to enclose your strings in PostgreSQL with singular quotes, not doubles. This one is correct: 'string here' for example. A syntax error will happen if you use doubles.

Finally, to quickly get away from a long results list or a command you started or completed, push CTRL+C.

Accessing PostgreSQL using the ‘psql’ command line interface

  • From your server on your localhost, connect to your database in PostgreSQL with the command psql.
psql postgres
  • Alternatively to the above command, input your username, host, and then database name to make a Postgres database connection.
psql -U some_username -h 127.0.0.1 -d some_database

NOTE: See the flags in the above code.

  • Your username in Postgres comes after the flag -U
  • The IP address or host domain goes after the flag -h
  • The database PostgreSQL name is inputted after the flag -d

PostgreSQL cheat sheet of useful SQL queries and commands

This PostgreSQL cheat sheet contains some of the most frequently-used commands to perform basic computing software programming functions so that you can code with efficiency.

Use ‘SELECT’ to get a Postgres table’s column names

  • Obtain the names of a table’s columns with the information_schema command:
SELECT*FROM information_schema.columns
WHERE some_table ='some_table';
  • You can also access the names of a public table’s column with the table_schema command:
SELECT*FROM information_schema.columns
WHERE table_schema ='public'
AND some_table ='some_table';

PostgreSQL cheat sheet commands for modifying tables

  • Use the INSERT INTO statement to add a value to a table:
INSERTINTO some_table(col1, col2)VALUES(value1,value2);

NOTE: The above command adds two columns and two values. See (col1, col2) and (value1, value2) in the SQL statement. Place a comma after each indicated column or value within the parenthesis when you have more than one to add to a table.

  • Use the INSERT INTO and SELECT statement to add a table’s column data to a different table:
INSERTINTO table1(column_list)SELECT column_list FROM table2;
  • Save table updates with the UPDATE statement:
  • Use the UPDATE statement for condition matching in a table:
UPDATE some_table SET col1 = new_val, col2 = new_val WHERE condition;
  • Use the DELETE FROM statement to remove all records from a table in Postgres:

NOTE: An option to remove all records from a table in Postgres is to use the command TRUNCATE followed by naming the table you want to delete.

  • Use the DELETE FROM statement to remove data pertaining to a condition:
DELETEFROM some_table
WHERE condition;

PostgreSQL cheat sheet for managing databases

  • Make a database with the CREATE DATABASE statement:

NOTE: A database may already exist, so to avoid raising an exception, use the IF NOT EXISTS clause after the CREATE DATABASE statement.

  • Use DROP DATABASE to delete a database forever:
DROPDATABASE[IFNOTEXISTS] db_name;

NOTE: You won’t get an error message prompt if you add the IF NOT EXISTS clause.

Use the a PostgreSQL ‘SELECT’ statement to query data

Query data in a table with these various SELECT statement command.

  • Add the wildcard asterisk * symbol to have every record in a PostgreSQL table return in the results page.
  • Indicate which columns to query:
SELECT col1, col2 FROM some_table;
  • Query a filtered table:
  • Include the clause WHERE to specify the columns you want to query:
SELECT some_col, another_col FROM some_table
WHERE some_int >50;
  • Perform a column query and give the column an alias with this statement:

Here are some commands to query in PostgreSQL using operators.

Psql Commands

  • Use the operator LIKE to query a character string pattern match:
Postgresql Command Line Cheat Sheet

To query a set of operations in PostgreSQL:

Using the LIKE operator:

SELECT*FROM some_table
WHERECOLUMNLIKE'%value';
  • Use the operator BETWEEN to query a table range:
SELECT*FROM some_table WHERECOLUMNBETWEEN low AND high;
  • Use the operator IN to add more than one condition or value to your WHERE clause in your statement:
SELECT*FROM some_table WHERECOLUMNIN(value1, value2);
  • Use the operator UNION to merge at least two SELECT statement results sets.
  • Use the operator EXCEPT to put together two SELECT statements that will only return rows that are not in the second statement.
SELECT*FROM table1 EXCEPTSELECT*FROM table2;
  • Use the operator INTERSECT to have the results set to reflect every record picked by at least two statements. If a record fails to match each query, it won’t appear in the results set:
  • Use the clause LIMIT to return a limited amount of rows. In the statement below, OFFSET rows are skipped:
SELECT*FROM some_table
LIMITLIMIT OFFSET offset
ORDERBY column_name;

Here are a few SQL statements for querying multiple tables.

  • Make a multiple Postgres table query with the INNER JOIN statement:
SELECT*FROM table1 INNERJOIN table2 ON conditions
  • Make a multiple Postgres table query with the LEFT JOIN statement:
  • Make a multiple Postgres table query with the FULL OUTER JOIN statement:
SELECT*FROM table1 FULLOUTERJOIN table2 ON conditions
  • Make a multiple Postgres table query with the CROSSJOIN statement:
SELECT*FROM table1 CROSSJOIN table2 ON conditions
  • Make a multiple Postgres table query with the NATURAL JOIN statement:
SELECT*FROM table1 NATURALJOIN table2 ON conditions

Here are a few common SELECT statements for displaying table rows.

  • Use the wildcard (*) to show all table rows:
  • Use the ORDER BY clause to sort the order of table rows in the results:
SELECT column_name FROM some_table ORDERBY column_name [ASC|DESC];
  • To group table data, use the clause GROUP BY:
Cheat
  • Use both clauses HAVING and GROUP BY to specify the criteria for grouping the data results:
SELECT*FROM some_table GROUPBY col1 HAVING condition;

Conclusion on the PostgreSQL cheat sheet

A helpful PostgreSQL cheat sheet is meant to help you reduce the time you spend on your daily coding projects. Make it an accessible reference of common SQL statements and other commands are at your fingertips. This way, you won’t have to wonder if the syntax is off the mark. The most beneficial result is that you’ll likely cut down on unnecessarily raised exceptions every day.

PostgreSQL Commond Line Cheat Sheet

##General Postgres Command

change to postgres user and open psql prompt

>sudo -u postgres psql postgres

Postgresql Command Line Cheat Sheet Free

password “test”

show postgres versoin

>postgres=# SELECT version();

list databases

>postgres=# l

connect to database

>postgres=# c <databasename>

switch to different database with role <role-name>

>postgres=# c <databasename> <role-name>

list tables in connected database

>postgres=# dt

list columns on table

>postgres=# d <tablename>

exit console

>postgres=# Ctrl-D or q

##Performance tuning

turn on query timing

>postgres=# timing

analyze query

>postgres=# EXPLAIN ANALYZE SELECT COUNT(*) FROM hm_client_session;

look at locks

fast count estimate rows in a table

>reportingdb_1=# SELECT reltuples::bigint AS estimate FROM pg_class where relname=’hm_client_session’;

estimate

———-

7375553

(1 row)

Time: 0.710 ms

##configdb check

connect to database

>postgres=# c configdb_1

copy query output as CSV to file

>configdb_1=# Copy (SELECT * FROM hm_device WHERE is_connected=false) To ‘/tmp/hm_device.csv’ with CSV HEADER;

drop database

>postgres=# DROP DATABASE demodb1;

## Backup and restore database

> pg_dump -i-h localhost -p5432-U postgres -F t -b-v-f“~/backups/backup-file.backup” database_name_to_backup

–i, –ignore-version proceed even when server version mismatches. Usefulwhile migrating data between servers. –h localhost, host to connect, can be IP address –p 5432, default port used by PostgreSQL–U postgres, this is default username, make sure user has rights to backup database –F t, -format used for backup, I suggest always using “t” (tar), other options are listed below –b, –blobs include large objects in dump –v, –verbose –f “~/backups/test-database.backup”, file where backup will be stored database_name_to_backup, database name which we want to backup

>pg_restore -i-h localhost -p5432-U postgres -d old_db -v“~/backups/backup-file.backup”

–p, –port=PORT database server port number –i, –ignore-version proceed even when server version mismatches –h, –host=HOSTNAME database server host or socket directory –U, –username=NAME connect as specified database user –W, –password force password prompt (should happen automatically) –d, –dbname=NAME connect to database name –v, –verbose verbose mode

Cheat

## Privilege and Roles

list roles

>postgres=# du

create role

>postgres=# CREATE ROLE demorole1 WITH LOGIN ENCRYPTED PASSWORD ‘password1’ CREATEDB;

create role with multiple privileges

>postgres=# CREATE ROLE demorole1 WITH LOGIN ENCRYPTED PASSWORD

>postgres=# ‘password1’ CREATEDB CREATEROLE REPLICATION SUPERUSER;

alter role

>postgres=# ALTER ROLE demorole1 CREATEROLE CREATEDB REPLICATION SUPERUSER;

drop role

>postgres=# DROP ROLE demorole1;

create database

>postgres=# CREATE DATABASE demodb1 WITH OWNER demorole1 ENCODING ‘UTF8’;

grant privileges to new user

>postgres=# GRANT ALL PRIVILEGES ON DATABASE demodb1 TO demorole1;