Complete Course

SQL for Testers

Stop trusting the UI: query a real database to prove what the application actually stored, find the data bugs no interface shows you, and build your own test data.

~4 hours of content

View Lessons

Course Content

11 comprehensive lessons covering everything you need to know

Introduction

Course Structure

Learn how the course is organized and make the most of the content.

Introduction

Prerequisites

Systems and knowledge required to complete the course. No SQL background needed.

Introduction

Getting to know the application under test

Meet the blog application, its four tables, and the seed data you will query all course long.

Lesson

Lesson 1

Clone and open your first database session

Clone the project, start PostgreSQL in Docker, and run your first two commands at the prompt.

Reading data

Lesson

Lesson 2

The shape of a database

Tables, rows, columns, primary and foreign keys, and how to read a schema you did not write.

Lesson

Lesson 3

SELECT, WHERE, and ORDER BY

Build the query a tester writes every day, one clause at a time, and see why ORDER BY must be deterministic.

Lesson

Lesson 4

Filtering like a tester

IN, BETWEEN, LIKE, and ILIKE, plus the NULL behavior that silently drops rows from a correct-looking query.

Lesson

Lesson 5

Joins without fear

Inner versus left join explained by the bugs each one lets you see, and why joins multiply rows.

Answering testing questions

Lesson

Lesson 6

Aggregations and GROUP BY

Verify the numbers an application displays with COUNT, GROUP BY, and HAVING, and avoid the counts that lie.

Lesson

Lesson 7

Finding data problems

Hunt duplicates, orphans, broken references, and impossible states, using anomalies you create yourself.

Lesson

Lesson 8

Verifying the UI against the database

Act in the app, query what persisted, and tell a display bug apart from a data bug.

Lesson

Lesson 9

Building and cleaning test data

INSERT, UPDATE, DELETE, and transactions, with the professional norms that keep you out of trouble.

Working professionally

Lesson

Lesson 10

Why a query is slow

Indexes, EXPLAIN and EXPLAIN ANALYZE, sequential versus index scans, and the database-side N+1.

Lesson

Lesson 11

SQL in automated tests

When a database assertion makes a test sharper, when it makes it brittle, and how to seed from test code.

Bonus & Conclusion

Bonus

Bonus: SQL questions in QA interviews

The SQL questions that actually come up in QA hiring, with worked answers you can run on the blog schema.

Conclusion

Congratulations!

You've completed the SQL for Testers course!