SQL Basics Cheat Sheet

The Different Dialects of SQL

Although SQL languages all share a basic structure, some of the specific commands and styles can differ slightly. Popular dialects include MySQL, SQLite, SQL Server, Oracle SQL, and more. PostgreSQL is a good place to start —since it’s close to standard SQL syntax and is easily adapted to other dialects. 

Sample Data

Throughout this cheat sheet, we'll be using the sample data airbnb_listings—denoting rental apartments on Airbnb.

Querying tables

Get all the columns from a table

SELECT * 
FROM airbnb_listings;Obsługiwane przez

Return the city column from the table

SELECT city 
FROM airbnb_listings;Obsługiwane przez

Get the city and year_listed columns from the table

SELECT city, year_listed
FROM airbnb_listings;
Obsługiwane przez

Get the listing id, city, ordered by the number_of_rooms in ascending order

SELECT city, year_listed 
FROM airbnb_listings 
ORDER BY number_of_rooms ASC;
Obsługiwane przez

Get the listing id, city, ordered by the number_of_rooms in descending order

SELECT city, year_listed 
FROM airbnb_listings 
ORDER BY number_of_rooms DESC;
Obsługiwane przez

Get the first 5 rows from airbnb_listings

SELECT * 
FROM airbnb_listings
LIMIT 5;
Obsługiwane przez

Get a unique list of cities where there are listings

SELECT DISTINCT city
FROM airbnb_listings;
Obsługiwane przez

Filtering on numeric columns

Get all the listings where number_of_rooms is more or equal to 3

SELECT *
FROM airbnb_listings 
WHERE number_of_rooms >= 3;Obsługiwane przez

Get all the listings where number_of_rooms is more than 3

SELECT *
FROM airbnb_listings 
WHERE number_of_rooms > 3;Obsługiwane przez

Get all the listings where number_of_rooms is exactly 3

SELECT *
FROM airbnb_listings 
WHERE number_of_rooms = 3;Obsługiwane przez

Get all the listings where number_of_rooms is lower or equal to 3

SELECT *
FROM airbnb_listings 
WHERE number_of_rooms <= 3;Obsługiwane przez

Get all the listings where number_of_rooms is lower than 3

SELECT *
FROM airbnb_listings 
WHERE number_of_rooms < 3;Obsługiwane przez

Filtering columns within a range—Get all the listings with 3 to 6 rooms

SELECT *
FROM airbnb_listings 
WHERE number_of_rooms BETWEEN 3 AND 6;Obsługiwane przez

Filtering on text columns

Get all the listings that are based in 'Paris'

SELECT * 
FROM airbnb_listings 
WHERE city = 'Paris';
Obsługiwane przez

Filter one column on many conditions—Get the listings based in the 'USA' and in ‘France’

SELECT *
FROM airbnb_listings 
WHERE country IN ('USA', 'France');Obsługiwane przez

Get all listings where city starts with "j" and where it does not end with "t"

SELECT * 
FROM airbnb_listings 
WHERE city LIKE 'j%' AND city NOT LIKE '%t';
Obsługiwane przez

Filtering on multiple columns

Get all the listings in "Paris" where number_of_rooms is bigger than 3

SELECT *
FROM airbnb_listings 
WHERE city = 'Paris' AND number_of_rooms > 3;
Obsługiwane przez

Get all the listings in "Paris" OR the ones that were listed after 2012

SELECT * 
FROM airbnb_listings
WHERE city = 'Paris' OR year_listed > 2012;Obsługiwane przez

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Filtering on missing data

Get all the listings where number_of_rooms is missing

SELECT *
FROM airbnb_listings 
WHERE number_of_rooms IS NULL; 
Obsługiwane przez

Get all the listings where number_of_rooms is not missing

SELECT *
FROM airbnb_listings 
WHERE number_of_rooms IS NOT NULL; 
Obsługiwane przez

Simple aggregations

Get the total number of rooms available across all listings 

SELECT SUM(number_of_rooms) 
FROM airbnb_listings; Obsługiwane przez

Get the average number of rooms per listing across all listings

SELECT AVG(number_of_rooms) 
FROM airbnb_listings;
Obsługiwane przez

Get the listing with the highest number of rooms across all listings

SELECT MAX(number_of_rooms) 
FROM airbnb_listings;Obsługiwane przez

Get the listing with the lowest number of rooms across all listings

SELECT MIN(number_of_rooms) 
FROM airbnb_listings;
Obsługiwane przez

Grouping, filtering, and sorting 

Get the total number of rooms for each country

SELECT country, SUM(number_of_rooms)
FROM airbnb_listings
GROUP BY country;Obsługiwane przez

Get the average number of rooms for each country

SELECT country, AVG(number_of_rooms)
FROM airbnb_listings
GROUP BY country;Obsługiwane przez

Get the listing with the maximum number of rooms for each country

SELECT country, MAX(number_of_rooms)
FROM airbnb_listings
GROUP BY country;Obsługiwane przez

Get the listing with the lowest amount of rooms per country

SELECT country, MIN(number_of_rooms)
FROM airbnb_listings
GROUP BY country;Obsługiwane przez

For each country, get the average number of rooms per listing, sorted by ascending order

SELECT country, AVG(number_of_rooms) AS avg_rooms
FROM airbnb_listings
GROUP BY country
ORDER BY avg_rooms ASC;Obsługiwane przez

For Japan and the USA, get the average number of rooms per listing in each country

SELECT country, AVG(number_of_rooms)
FROM airbnb_listings
WHERE country IN ('USA', 'Japan');
GROUP BY country;Obsługiwane przez

Get the number of listings per country

SELECT country, COUNT(id) AS number_of_listings
FROM airbnb_listings
GROUP BY country;Obsługiwane przez

Get all the years where there were more than 100 listings per year

SELECT year_listed
FROM airbnb_listings
GROUP BY year_listed
HAVING COUNT(id) > 100;Obsługiwane przez