Image by freepik
As a data professional, you will use SQL all the time. But even if you know SQL, it can be useful to have a quick reference to look up certain syntaxes and use cases.
Here is a collection of five very useful SQL cheat sheets/references covering the following topics:
- SQL Basics
- Data preparation with SQL
- SQL joins
- SQL window functions
- SQL interview questions
Then let's get started!
You can learn the basics of SQL in a few hours. You just need to familiarize yourself with the syntax and then practice solving some questions to apply the concepts you just learned. And if you need a refresher on topics such as filtering using operators, combination types, grouping and aggregation functions, you can consult the SQL Basics LearnSQL Cheat Sheet.
Topics covered include:
- Query a single table
- Filter output
- Query multiple tables
- Aggregation and grouping
- Subqueries
- Set operations
Link: SQL Basics Cheat Sheet – LearnSQL
For any data science project, data preparation is very important. Stan Pugsley's SQL Data Preparation Cheat Sheet for KDnuggets will help you review key SQL data preparation techniques.
You can review how to perform the following data preparation tasks with SQL:
- Profile Data Sets
- Validate attributes
- Standardize attributes
- Create attributes
- Derive attributes
- Combine data sets
- Split data sets
Link: Data Preparation with SQL Cheat Sheet – KDnuggets
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, the joints may seem quite difficult until you have practiced enough.
He SQL Joins The DataCamp Cheat Sheet is a quick reference that covers the following join types:
- Join internally
- auto join
- join the left
- Join completely
- cross join
And the following set theory operators in SQL:
- Union
- union all
- intersect
- Except
Link: SQL Joins Cheat Sheet – DataCamp
If you've learned the basics of SQL, you should be comfortable using aggregate functions. Applying the 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 allow you to calculate quantities between 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, cumulative sum, and the like.
Window functions are also extremely important if you are preparing for an interview. He SQL window functions The DataCamp cheat sheet will help you quickly review the functions of the SQL window. First review the following:
- Window function syntax.
- ORDER BY and PARTITION BY clauses
- Window frame extension
The cheat sheet also covers the following categories of window functions:
- Sorting Window Features
- Values Window Functions
- Added window functions
- Advance and delay
Link: SQL Window Functions Cheat Sheet – DataCamp
Now this is No A cheat sheet, but more of a useful reference for frequently asked interview questions. It is intended to be a quick review to check your understanding of the fundamental concepts.
This SQL Interview Questions The Edureka collection has several questions on database basics such as relationships, schemas, constraints, and more. Which you should definitely be familiar with if you have any experience working with relational databases.
Additionally, you also have some questions on the following topics:
- Standardization
- 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
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 master SQL, practice is as necessary as learning. In fact, the practice should be a part of the learning process. So if you are looking for good platforms to practice SQL, check out the 7 Best Platforms to Practice SQL collection.
Bala Priya C. is a developer and technical writer from India. He enjoys working at the intersection of mathematics, programming, data science, and content creation. His areas of interest and expertise include DevOps, data science, and natural language processing. He likes to read, write, code and drink coffee! Currently, he is working to learn and share his knowledge with the developer community by creating tutorials, how-to guides, opinion pieces, and more.
