SQL · Chapter 1 of 42

SQL Introduction

SQL (Structured Query Language) is the standard language for storing, querying and updating data in relational databases such as MySQL, PostgreSQL, SQL Server, Oracle and SQLite.

Even though each vendor has small syntax differences, ~90% of SQL is portable across all of them.

What SQL does

SELECT to read, INSERT to add, UPDATE to change, DELETE to remove. These are the four core operations (CRUD).

Where you'll use it

Backend development, data analysis, business intelligence, machine learning pipelines — anywhere structured data lives.

Example 1 (sql)

SELECT name, age FROM users WHERE age > 18;

Output

name    | age
Ana     | 25
Ben     | 30

Read specific columns with a filter.

Example 2 (sql)

INSERT INTO users (name, age) VALUES ('Cara', 22);

Output

1 row inserted

Add one row to a table.

Key points

SQL = Structured Query Language.
Used with relational databases (rows and columns).
Core operations: SELECT, INSERT, UPDATE, DELETE.
Keywords are case-insensitive; data is case-sensitive.

💡 Note: SQL is declarative — you describe WHAT you want, and the database engine figures out HOW to fetch it.

SQL Introduction

What SQL does

Where you'll use it

Key points

📝 Quick Quiz