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As a data professional, you’ll use SQL all the time. But even if you know SQL, it can be helpful to have a quick reference to look up certain syntaxes and use cases.

Here’s a collection of five super helpful SQL cheat sheets/references covering the following topics:

• SQL basics 
• Data preparation with SQL 
• SQL joins 
• SQL window functions 
• SQL interview questions 

So let's get started!

1. SQL Basics

You can learn SQL basics in a few hours. You only need to familiarize yourself with the syntax and then practice solving a few questions to apply the concepts you just learned. And if you need a refresher on topics like filtering using operators, the join types, group by and aggregate functions, you can refer to the SQL Basics cheat sheet by LearnSQL.

The topics covered include:

• Querying a single table
• Filtering the output
• Querying multiple tables
• Aggregation and grouping
• Subqueries
• Set operations

Link: SQL Basics Cheat Sheet – LearnSQL

2. Data Preparation with SQL

For any data science project, data preparation is super important. The Data Preparation with SQL cheat sheet by Stan Pugsley for KDnuggets will help you go over the key data preparation techniques with SQL.

You can review how to perform the following data prep tasks with SQL:

• Profile datasets 
• Validate attributes 
• Standardize attributes 
• Create attributes 
• Derive attributes 
• Combine datasets 
• Split datasets

Link: Data Preparation with SQL Cheat Sheet – KDnuggets

3. SQL Joins

Joins in SQL are quite common when you have to use information from multiple database tables to answer the question at hand. But if you are a beginner, joins can seem quite difficult until you’ve practiced enough.

The SQL Joins cheat sheet by DataCamp is a quick reference that covers the following join types:

• Inner join
• Self join 
• Left join
• Full join 
• Cross join 

And the following set theory operators in SQL:

• Union 
• Union all 
• intersect 
• Except

Link: SQL Joins Cheat Sheet – DataCamp

4. SQL Window Functions

If you’ve learned the basics of SQL, you should be comfortable using aggregate functions. Applying aggregate function on a column reduces the set of rows to the specific value such as the average, minimum, and maximum values. 

Like aggregate functions, window functions also let you calculate quantities across values in a column, but the result is not reduced to a single value. Rather they return a set of rows. Examples include moving average, running sum, and the like. 

Window functions are also extremely important if you’re preparing for interviews. The SQL Window Functions cheat sheet by DataCamp will help you quickly review SQL window functions. It first goes over the following:

• Syntax of window functions 
• ORDER BY and PARTITION BY clauses
• Window frame extent 

The cheat sheet also covers the following categories of window functions:

• Ranking window functions 
• Value window functions 
• Aggregate window functions 
• LEAD and LAG

Link: SQL Window Functions Cheat Sheet – DataCamp

5. SQL Interview Questions

Now this is not a cheat sheet but more of a helpful reference for commonly-asked interview questions. It’s meant to be a quick refresher to check your understanding of the foundational concepts. 

This SQL Interview Questions collection from Edureka has several questions on the basics of databases such as relationships, schema, constraints, and more. Which you should definitely be familiar with if you have some experience working with relational databases.

In addition, you have some questions on the following topics as well:

• Normalization
• OLAP vs. OLTP systems
• Types of database indexes
• Query optimization
• Database triggers
• Subquery
• Stored procedures
• SQL Server and PostgreSQL-specific questions

Link: Top 115 SQL Interview Questions – Edureka

Wrapping Up

Whether you're using SQL at work, learning SQL, or need a quick refresher before your next interview, I'm sure these cheat sheets will help you review what you need. 

But to become proficient in SQL, practice is just as necessary as learning. In fact, practice should be a part of the learning process. So if you're looking for good platforms to practice SQL, check out the compilation 7 Best Platforms to Practice SQL.
 
 

Bala Priya C is a developer and technical writer from India. She likes working at the intersection of math, programming, data science, and content creation. Her areas of interest and expertise include DevOps, data science, and natural language processing. She enjoys reading, writing, coding, and coffee! Currently, she's working on learning and sharing her knowledge with the developer community by authoring tutorials, how-to guides, opinion pieces, and more. Bala also creates engaging resource overviews and coding tutorials.