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Introduction

Basic SQL
≈ 2 min read

Welcome to SQL!

Almost every backend application eventually starts working with data. Users, orders, payments, products, settings — all of this needs to be stored, searched, changed, and connected. This is where SQL comes in.

At first, queries can look like a collection of keywords: SELECT, WHERE, JOIN, GROUP BY. But behind them is a fairly consistent model for working with tables and data. The goal of the course is to teach you to see that model instead of simply memorizing query templates.

As you move through the course, you will:

  • read and write SQL queries from simple selections to more complex combinations of data;
  • understand how filtering, sorting, grouping, and joins change the query result;
  • learn about keys, constraints, indexes, transactions, and other database mechanisms;
  • learn to find mistakes in queries and understand why one approach works better than another.

How to get the most out of the course

The routine is simple: study a topic → write a few queries → check yourself through practice → return to the difficult part if something is still unclear. SQL is best reinforced not by reading, but by constantly working with small data sets.

Do not learn SQL as a set of commands. Each time, try to understand which rows participate in the query, what happens to them at each stage, and what result the database should return.
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