Postgresql Queries Cheat Sheet

Structured Query Language (SQL) is a set-based language as opposed to a procedural language. It is the defacto language of relational databases.

Postgresql Psql Commands
Postgresql Queries Cheat Sheet Pdf
Postgresql Queries Cheat Sheet Example
Postgresql Queries Cheat Sheet 2019
Postgres Json Query Cheat Sheet
Postgresql Commands Cheat Sheet
Postgresql Query Example

The PostgreSQL cheat sheet page provides you with the common PostgreSQL commands and statements that enable you to work with PostgreSQL quickly and effectively. Oracle Linux Virtualization Manager (OLVM) Engine PostgreSQL Database Queries Cheat Sheet. This post will explain some practical psql commands and describe how to run the PostgreSQL queries from the command line to get useful information from the engine database.

The difference between a set-based language vs. a procedural language is that in a set-based language you define what set of data you want or want to operate on and the atomic operation to apply to each element of the set. You leave it up to the Database process to decide how best to collect that data and apply your operations. In a procedural language, you basically map out step by step loop by loop how you collect and update that data.
There are two main reasons why SQL is often better to use than procedural code.

It is often much shorter to write - you can do an update or summary procedure in one line of code that would take you several lines of procedural.
For set-based problems - SQL is much faster processor-wise and IO wise too because all the underlining looping iteration is delegated to a database server process that does it in a very low level way and uses IO/processor more efficiently and knows the current state of the data - e.g. what other processes are asking for the data.

Example SQL vs. Procedural

If you were to update say a sales person of all customers in a particular region - your procedural way would look something like this

The SQL way would be:
UPDATE customers SET salesperson = 'Mike' WHERE state = 'NH'

If you had say 2 or 3 tables you need to check, your procedural quickly becomes difficult to manage as you pile on nested loop after loop.
In this article we will provide some common data questions and processes that SQL is well suited for and SQL solutions to these tasks. Most of these examples are fairly standard ANSI-SQL so should work on most relational databases such as IBM DBII, PostGreSQL, MySQL, Microsoft SQL Server, Oracle, Microsoft Access, SQLite with little change. Some examples involving subselects or complex joins or the more complex updates involving 2 or more tables may not work in less advanced relational databases such as MySQL, MSAccess or SQLite. These examples are most useful for people already familiar with SQL. We will not go into any detail about how these work and why they work, but leave it up to the reader as an intellectual exercise. What customers have bought from us?

Example: What customers have never ordered anything from us?

SELECT customers.* FROM customers LEFT JOIN orders ON customers.customer_id = orders.customer_id WHERE orders.customer_id IS NULL

More advanced example using a complex join: What customers have not ordered anything from us in the year 2004 - this one may not work in some lower relational databases (may have to use an IN clause)

SELECT customers.* FROM customers LEFT JOIN orders ON (customers.customer_id = orders.customer_id AND year(orders.order_date) = 2004) WHERE orders.order_id IS NULL

Please note that year is not an ANSI-SQL function and that many databases do not support it, but have alternative ways of doing the same thing.

SQL Server, MS Access, MySQL support year().
PostGreSQL you do date_part('year', orders.order_date)
SQLite - substr(orders.order_date,1,4) - If you store the date in form YYYY-MM-DD
Oracle - EXTRACT(YEAR FROM order_date) or to_char(order_date,'YYYY')

Note: You can also do the above with an IN clause, but an IN tends to be slower
Same question with an IN clause

SELECT customers.* FROM customers WHERE customers.customer_id NOT IN(SELECT customer_id FROM orders WHERE year(orders.order_date) = 2004)

How many customers do we have in Massachusetts and California?

 SELECT customer_state As state, COUNT(customer_id) As total FROM customers WHERE customer_state IN('MA', 'CA') GROUP BY customer_state

What states do we have more than 5 customers?

How many states do we have customers in?

_{Note the above does not work in Microsoft Access or SQLite - they do not support COUNT(DISTINCT ..)}
Alternative but slower approach for the above - for databases that don't support COUNT(DISTINCT ..), but support derived tablesList in descending order of orders placed customers that have placed more than 5 orders
Value Insert

Copy data from one table to another table

Creating a new table with a bulk insert from another table
Update from values
UPDATE customers SET customer_salesperson = 'Billy' WHERE customer_state = 'TX'
Update based on information from another table

 UPDATE customers SET rating = 'Good' FROM orders WHERE orderdate > '2005-01-01' and orders.customer_id = customers.customer_id

_{Please note the date format varies depending on the database you are using and what date format you have it set to.}
Update based on information from a derived table
_{Please note the update examples involving additional tables do not work in MySQL, MSAccess, SQLite.}
MS Access Specific syntax for doing multi-table UPDATE joins
UPDATE customers INNER JOIN orders ON customers.customer_id = orders.customer_id SET customers.rating = 'Good'
MySQL 5 Specific syntax for doing multi-table UPDATE joins
UPDATE customers, orders SET customers.rating = 'Good' WHERE orders.customer_id = customers.customer_id

Articles of Interest
PostgreSQL 8.3 Cheat Sheet	Summary of new and old PostgreSQL functions and SQL constructs complete xml query and export, and other new 8.3 features, with examples.
SQLite	If you are looking for a free and lite fairly SQL-92 compliant relational database, look no further. SQLite has ODBC drivers, PHP 5 already comes with an embedded SQLite driver, there are .NET drivers, freely available GUIs , and this will run on most Oses. All the data is stored in a single .db file so if you have a writeable folder and the drivers, that’s all you need. So when you want something lite and don't want to go thru a database server install as you would have to with MySQL, MSSSQL, Oracle, PostgreSQL, or don't have admin access to your webserver and you don't need database group user permissions infrastructure, this is very useful. It also makes a nice transport mechanism for relational data as the size the db file is pretty much only limited to what your OS will allow for a file (or 2 terabytes which ever is lower).
PostgreSQL Date Functions	Summary of PostGresql Date functions in 8.0 version
The Future of SQL by Craig Mullins	Provides a very good definition of what set-based operations are and why SQL is superior for these tasks over procedural, as well as a brief history of the language.
Summarizing data with SQL (Structured Query Language)	Article that defines all the components of an SQL statement for grouping data. We wrote it a couple of years ago, but it is still very applicable today.
Procedural Versus Declarative Languages	Provides some useful anlaogies for thinking about the differences between procedural languages and a declarative language such as SQL
PostgreSQL Cheat Sheet	Cheat sheet for common PostgreSQL tasks such as granting user rights, backing up databases, table maintenance, DDL commands (create, alter etc.), limit queries
MySQL Cheat Sheet	Covers MySQL datatypes, standard queries, functions
Comparison of different SQL implementations	This is a great summary of the different offerings of Standard SQL, PostGreSQL, DB2, MSSQL, MySQL, and Oracle. It demonstrates by clear example how each conforms or deviates from the ANSI SQL Standards with join syntax, limit syntaxx, views, inserts, boolean, handling of NULLS

title: PostgreSQLicon: icon-postgresbackground: bg-blue-800tags:

nullcategories:
Databasedate: 2021-01-11 14:19:24intro: |The PostgreSQL cheat sheet provides you with the common PostgreSQL commands and statements.

Getting started {.cols-3}

Getting started

Switch and connect

Postgresql Psql Commands

List all databases

Connect to the database named postgres

Disconnect

psql commands {.col-span-2}

Option	Example	Description
`[-d] <database>`	psql -d mydb	Connecting to database
`-U`	psql -U john mydb	Connecting as a specific user
`-h-p`	psql -h localhost -p 5432 mydb	Connecting to a host/port
`-U-h-p-d`	psql -U admin -h 192.168.1.5 -p 2506 -d mydb	Connect remote PostgreSQL
`-W`	psql -W mydb	Force password
`-c`	psql -c 'c postgres' -c 'dt'	Execute a SQL query or command
`-H`	psql -c 'l+' -H postgres > database.html	Generate HTML report
`-l`	psql -l	List all databases
`-f`	psql mydb -f file.sql	Execute commands from a file
`-V`	psql -V	Print the psql version
{.show-header}

Getting help

-	-
`h`	Help on syntax of SQL commands
`h` DELETE	DELETE SQL statement syntax
`?`	List of PostgreSQL command

Run in PostgreSQL console

Working {.cols-3}

Recon

Show version

Show system status

Show environmental variables

List users

Show current user

Show current user's permissions

Show current database

Show all tables in database

List functions

Databases

List databases

Connect to database

Show current database

Tables

List tables, in current db

List tables, globally

List table schema

Create table, with an auto-incrementing primary key

Permissions

Become the postgres user, if you have permission errors

Grant all permissions on database

Grant connection permissions on database

Grant permissions on schema

Grant permissions to functions

Grant permissions to select, update, insert, delete, on a all tables

Grant permissions, on a table

Grant permissions, to select, on a table

Columns

Update column

Delete column

Update column to be an auto-incrementing primary key

Insert into a table, with an auto-incrementing primary key

Data

[Select](http://www.postgresql.org/docs/current/static/sql-select.html] all data

Read one row of data

Search for data

Insert data

Update data

Delete all data

Delete specific data

Users

List roles

Alter user password