What is SQL? SQL, short for Structured Query Language, is the standard language for talking to databases. It is how you ask a database for information, add new information, change it, or remove it. Every app you use, from a music service to a bank, stores its information in a database, and SQL is the set of commands developers use to work with that data. If you have ever wanted to understand how apps remember your account, your orders or your friends, learning what is SQL is a good starting point.
SQL is also the most useful first language for anyone interested in data. It is simpler than a programming language such as Python or JavaScript, it is used by almost every large company, and you can learn the basics in a weekend. This guide explains what is SQL in plain English, how databases store information, the five basic commands, how SQL relates to other tools, and how to start learning it yourself.
What Is a Database?
A database is an organised store of information that a computer can search quickly. Think of a spreadsheet with a table for every kind of thing an app needs to remember. A shop app might have one table for customers, one for products and one for orders. Each table is made of columns, which describe the kind of information kept, and rows, which are the individual records.
For example, a customers table might have columns for name, email and city, and each row is one customer. An orders table might have columns for order number, date, customer and total. The real power comes from links between tables. An order row points to the customer who placed it and the products they bought, so the app can answer questions such as how much did this customer spend this year, or which products sell best in December.
What Is SQL, Exactly?
SQL is the language you use to ask questions of a database and to change it. The key idea is that you describe what you want, not how to get it. You say give me the names of all customers in Paris, and the database works out exactly where to look, which is the job of a program called a database management system, such as MySQL, PostgreSQL, SQL Server or SQLite.
SQL was created in the 1970s, and it has stayed almost the same since then, because it does its job well. It is not a general-purpose programming language, because it is not meant for building apps on its own. It is a specialised language for one important task: working with structured data. That is why, in software jobs from data analyst to web developer, SQL is one of the skills most often asked for. For more background, see the Wikipedia article on SQL.
How SQL Works: A Query, Step by Step
Imagine a library database with a table of books, with columns for title, author and year. If you want to find every book by J.K. Rowling, you write a query, which is a sentence in SQL. A typical one looks like this:
SELECT title, year FROM books WHERE author = 'J.K. Rowling';
First, SELECT tells the database which columns you want. Second, FROM tells it which table to look in. Third, WHERE filters the rows, so you only get the ones that match. The database runs the query, checks every row, and returns a table of results. The whole process takes a fraction of a second, even when the table has millions of rows, because the database uses indexes, like the index at the back of a book, to find things fast.
The five commands that cover most of the work are these. SELECT reads data from a table. INSERT adds a new row. UPDATE changes an existing row. DELETE removes a row. CREATE TABLE builds a new table. With those five, plus a few helpers for counting and sorting, you can build and run useful queries. If you have learned to use an API, you know a similar idea: an app sends a request and gets data back. SQL is the request language that runs behind many APIs.
SQL vs NoSQL
| SQL databases | NoSQL databases | |
|---|---|---|
| Data model | Fixed tables with rows and columns | Flexible, such as documents or key-value pairs |
| Best for | Structured data that must be correct, such as money and orders | Large, changing data, such as social media posts and logs |
| Example | MySQL, PostgreSQL, SQLite | MongoDB, Cassandra |
| Scaling | Run well on one powerful server, can scale up with effort | Designed to spread across many servers |
Both kinds have their place. A bank uses SQL databases because it needs bank balances to be correct, and the rules for SQL help make that happen. A social network uses NoSQL systems to store billions of posts and comments that change constantly. As a beginner, learn SQL first, because it teaches you the idea of tables and relationships, and it is easier to learn.
Where Is SQL Used?
SQL is everywhere data lives, which is almost everywhere. Every time you log in, buy something, check a delivery, or see a recommendation, a database query is running behind the scenes. Websites store user accounts in databases. Online shops store products and orders. Banks store transactions. Hospitals store patient records. Streaming services store films, users and viewing history, which is how they recommend what to watch next.
SQL is also used by data analysts, who write queries to answer business questions. How many people signed up last month? Which product had the best sales in each city? Which customers have not ordered for six months? Those are all SQL questions. Because data is at the centre of so many jobs, SQL is one of the few skills that is useful in software development, data analysis, research, marketing and finance, and it appears in job listings for each of them.
How to Learn SQL as a Beginner
Start with the five basic commands above. Practise them on a small data set, such as a list of films, books or football teams. The best way is to install a free tool such as SQLite or PostgreSQL, or use an online SQL playground in your browser. Write queries that answer real questions, such as which films came out after 2000, or which author has the most books. If you write a query that goes wrong, read the message from the database carefully; it will often tell you exactly what is wrong.
Once the basics feel easy, learn these features in order. First, sorting with ORDER BY and limiting with LIMIT, so you can see a top-10 list. Second, filtering with more conditions, such as AND and OR, and searching with LIKE. Third, grouping and counting with GROUP BY and COUNT, so you can answer how many of each thing there are. Fourth, joining two tables with JOIN, so you can combine orders and customers. Finally, learn to write safe queries, especially when you use data from users, because that is where most database security mistakes happen.
Do not try to learn every SQL feature at once. Most work uses only ten or fifteen commands, and experts use the same set every day. If you are also choosing a first programming language, read our comparison of Python vs JavaScript for beginners, which explains why SQL pairs well with either one.
Common Beginner Mistakes in SQL
The most common mistake is to forget the WHERE clause when you update or delete. An update without WHERE changes every row in the table, which can change every customer address at once. Always test an update or delete on a copy first, or add a test run before you run the real command.
Another common mistake is to store data in the wrong way, such as putting several values in one cell, or storing numbers as text. SQL works best when each fact has its own column and its own type. A third mistake is to use SELECT * when you only need a few columns. It is slow, it loads extra data, and it makes your results harder to read. The final mistake is to copy-and-paste SQL that you found online without understanding what it does. If you can explain a query in plain English, you will write a safe version of it, and you will catch most mistakes before they cause harm.
Conclusion
What is SQL? It is the standard language for working with databases. With a few simple commands, you can search millions of rows, add or change data, and answer real business questions. SQL works on the same idea everywhere, from a small app on your laptop to a data warehouse used by a global company, which is why it has lasted for fifty years.
SQL is the easiest first step into working with data. Learn SELECT, WHERE, INSERT, UPDATE and DELETE, practise on a data set that interests you, and then add joins, grouping and sorting. If you want to go further, read our guides to Git and Python for beginners, which show how SQL fits into the wider world of software development.
Frequently Asked Questions
What is SQL in simple words?
SQL is the language used to ask questions of a database and to change the data it stores. You use it to find, add, update and delete information in tables.
Is SQL a programming language?
Not in the usual sense. SQL is a query language, a specialised tool for databases. It is not used to build complete apps on its own, but it is used inside apps and by analysts.
Is SQL hard to learn?
No, it is one of the easiest technical skills to learn. You can write useful queries in a weekend, and most daily work uses only a small set of commands.
Do I need SQL if I learn Python?
Yes, for data work. Python is used to build apps and analyse data, and SQL is used to get that data in and out of a database. The two are usually learned and used together.
What is the difference between SQL and MySQL?
SQL is the language. MySQL is one database system that uses SQL, along with PostgreSQL, SQL Server and SQLite. Learning SQL works for all of them, and they differ mostly in small details.