SQL Basics Every Beginner Should Know

SQL (Structured Query Language) is the standard language for working with relational databases such as Oracle Database, MySQL and PostgreSQL. Developers, data analysts and testers all use it.

Start with SELECT. Read columns from a table, filter rows with WHERE and sort the result with ORDER BY. These three clauses answer a surprising number of questions.

Next, learn aggregation. Functions such as COUNT, SUM and AVG, combined with GROUP BY, turn thousands of rows into a short summary — for example, total sales per city.

Joins are the key step. Real data is split across tables, such as customers and orders. An INNER JOIN returns matching rows from both tables; a LEFT JOIN keeps every row from the first table even when there is no match.

Finally, practise changing data with INSERT, UPDATE and DELETE, and learn how primary keys and foreign keys protect your data. Practise a little every day on a small sample database and SQL will soon feel natural.