PostgreSQL Basics Cheat Sheet

What is PostgreSQL?

PostgreSQL is an open-source relational database management system (RDBMS) known for its extensibility and standards compliance. Developed and maintained by a group of volunteers known as The PostgreSQL Global Development Group, it is popular across a wide range of organizations from enterprises to government departments. It has powerful data analysis capabilities.

Sample Data

The dataset contains details of the world's fastest production cars by 0 to 60 mph acceleration time. Each row contains one car model, and the table is named cars.

Querying tables

Get all the columns from a table using SELECT *

SELECT *
	FROM cars

Get a column from a table by name using SELECT col

SELECT model
	FROM cars

Get multiple columns from a table by name using SELECT col1, col2

SELECT make, model
	FROM cars

Override column names with SELECT col AS new_name

SELECT make, model, propulsion_type AS engine_type
	FROM cars

Arrange the rows in ascending order of values in a column with ORDER BY col

SELECT  make, model, time_to_60_mph_s
	FROM cars
	ORDER BY time_to_60_mph_s

Arrange the rows in descending order of values in a column with ORDER BY col DESC

SELECT make, model, model_year
	FROM cars
	ORDER BY model_year DESC

Limit the number of rows returned with LIMIT n

SELECT *
	FROM cars
LIMIT 2

Get unique values with SELECT DISTINCT

SELECT DISTINCT propulsion_type
	FROM cars

Filtering Data

Filtering on numeric columns

Get rows where a number is greater than a value with WHERE col > n

SELECT make, model, time_to_60_mph_s
	FROM cars
	WHERE time_to_60_mph_s > 2.1

Get rows where a number is greater than or equal to a value with WHERE col >= n

SELECT make, model, time_to_60_mph_s
	FROM cars
	WHERE time_to_60_mph_s >= 2.1

Get rows where a number is less than a value with WHERE col < n

SELECT make, model, time_to_60_mph_s
	FROM cars
	WHERE time_to_60_mph_s < 2.1

Get rows where a number is less than or equal to a value with WHERE col <= n

SELECT make, model, time_to_60_mph_s
	FROM cars
	WHERE time_to_60_mph_s <= 2.1

Get rows where a number is equal to a value with WHERE col = n

SELECT make, model, time_to_60_mph_s
	FROM cars
	WHERE time_to_60_mph_s = 2.1

Get rows where a number is not equal to a value with WHERE col <> n or WHERE col != n

SELECT make, model, time_to_60_mph_s
	FROM cars
	WHERE time_to_60_mph_s <> 2.1

Get rows where a number is between two values (inclusive) with WHERE col BETWEEN m AND n

SELECT make, model, time_to_60_mph_s
	FROM cars
	WHERE time_to_60_mph_s BETWEEN 1.9 AND 2.1

Filtering on text columns

Get rows where text is equal to a value with WHERE col = 'x'

SELECT make, model, propulsion_type
	FROM cars
	WHERE propulsion_type = 'Hybrid'

Get rows where text is one of several values with WHERE col IN ('x', 'y')

SELECT make, model, propulsion_type
	FROM cars
	WHERE propulsion_type IN ('Electric',  'Hybrid')

Get rows where text contains specific letters with WHERE col LIKE '%abc%' (% represents any characters)

SELECT make, model, propulsion_type
	FROM cars
	WHERE propulsion_type LIKE '%ic%'

For case insensitive matching, use WHERE col ILIKE '%abc%'

SELECT make, model, propulsion_type
	FROM cars
	WHERE propulsion_type ILIKE '%ic%'

Filtering on multiple columns

Get the rows where one condition and another condition holds with WHERE condn1 AND condn2

SELECT make, model, propulsion_type, model_year
	FROM cars
	WHERE propulsion_type = 'Hybrid'
		AND model_year < 2020

Get the rows where one condition or another condition holds with WHERE condn1 OR condn2

SELECT make, model, propulsion_type, model_year
	FROM cars
	WHERE propulsion_type = 'Hybrid'
		OR model_year < 2020

Filtering on missing data

Get rows where values are missing with WHERE col IS NULL

SELECT make, model, limited_production_count
	FROM cars
	WHERE limited_production_count IS NULL

Get rows where values are not missing with WHERE col IS NOT NULL

SELECT make, model, limited_production_count
	FROM cars
	WHERE limited_production_count IS NOT NULL

Aggregating Data

Simple aggregations

Get the total number of rows SELECT COUNT(*)

SELECT COUNT(*)
	FROM cars

Get the total value of a column with SELECT SUM(col)

SELECT SUM(limited_production_count)
	FROM cars

Get the mean value of a column with SELECT AVG(col)

SELECT AVG(time_to_60_mph_s)
	FROM cars

Get the minimum value of a column with SELECT MIN(col)

SELECT MIN(time_to_60_mph_s)
	FROM cars

Get the maximum value of a column with SELECT MAX(col)

SELECT MAX(time_to_60_mph_s)
	FROM cars

Grouping, filtering, and sorting

Get summaries grouped by values with GROUP BY col

SELECT propulsion_type, COUNT(*)
	FROM cars
	GROUP BY propulsion_type

Get summaries grouped by values, in order of summaries with GROUP BY col ORDER BY smmry

SELECT propulsion_type, AVG(time_to_60_mph_s) AS mean_time_to_60_mph_s
	FROM cars
	GROUP BY propulsion_type
	ORDER BY mean_time_to_60_mph_s

Get rows where values in a group meet a criterion with GROUP BY col HAVING condn

SELECT propulsion_type, AVG(time_to_60_mph_s) AS mean_time_to_60_mph_s
	FROM cars
	GROUP BY propulsion_type
	HAVING mean_time_to_60_mph_s > 2

Filter before and after grouping with WHERE condn_before GROUP BY col HAVING condn_after

SELECT propulsion_type, AVG(time_to_60_mph_s) AS mean_time_to_60_mph_s
	FROM cars
WHERE limited_production_count IS NOT NULL
	GROUP BY propulsion_type
	HAVING mean_time_to_60_mph_s > 2

PostgreSQL-Specific Syntax

Not all code works in every dialect of SQL. The following examples work in PostgreSQL, but are not guaranteed to work in other dialects.

Limit the number of rows returned, offset from the top with LIMIT m OFFSET n

SELECT *
	FROM cars
LIMIT 2 OFFSET 3

PostgreSQL allows text concatenation with the || operator

SELECT make || ' ' || model AS make_and_model
 	FROM cars

Get the current date with CURRENT_DATE and the current datetime with NOW() or CURRENT_TIME

SELECT NOW(), CURRENT_DATE, CURRENT_TIME

List available tables by selecting from pg_catalog.pg_tables

SELECT * FROM pg_catalog.pg_tables