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Introduction to SQL

SQL (Structured Query Language) is the standard language for communicating with relational databases. Almost every data tool you'll encounter — data warehouses, BI platforms, dbt — speaks SQL under the hood.

Placeholder Lesson

This lesson is a work in progress. Content will be expanded with examples, exercises, and a video walkthrough.

What Is a Relational Database?​

A relational database organizes data into tables (rows and columns), similar to a spreadsheet. Each table represents one type of entity — for example, orders, customers, or products. Tables are linked together through keys.

Your First Query​

The most basic SQL query retrieves all rows from a table:

SELECT *
FROM orders;

To retrieve specific columns:

SELECT
    order_id,
    customer_id,
    order_date,
    total_amount
FROM orders;

Filtering Rows with WHERE​

Use WHERE to return only the rows that meet a condition:

SELECT
    order_id,
    customer_id,
    total_amount
FROM orders
WHERE total_amount > 100;

What's Next​

In the next lesson you'll learn how to aggregate data — counting rows, summing values, and grouping results.