SQL Basics for QA

SQL is a language that is impossible to imagine modern software testing without. In QA processes, a database often serves as the single source of truth: it stores the actual values that must match what the user sees in the UI. Being able to write queries, verify data, and detect discrepancies between application layers directly affects product quality and speeds up defect investigation. This course gives you practical SQL skills in the context of QA tasks, helping you move from passive observation to active data verification.

The program covers the full cycle of working with relational databases: from understanding table structure and data types to writing complex SELECT queries. You will learn how to filter rows with WHERE, sort with ORDER BY, group with GROUP BY, and use aggregate functions (COUNT, SUM, AVG, MIN, MAX). Special attention is paid to joining tables (INNER JOIN, LEFT JOIN, RIGHT JOIN) — a key skill for matching data from different sources. You will learn to use subqueries, the IN, BETWEEN, LIKE operators, and work with NULL values. Separate topics focus on finding discrepancies between the UI and the database: you will master methods for comparing query results with the data displayed in the UI, and learn how to determine whether a problem is a frontend or backend defect.

The course methodology is built on real cases from QA engineers’ practice. Each topic includes exercises that simulate typical real-world scenarios: checking data correctness after user registration, validating reports, and identifying duplicates and anomalies. You will also learn how to read and interpret data without documentation — a critical skill when working with legacy systems or projects with incomplete specifications. Common mistakes are covered: incorrect use of JOIN, confusion with NULL, improper grouping, and inefficient queries that can slow down testing.

The course is intended for junior QA engineers who want to deepen their knowledge in data verification; manual QA engineers who want to automate part of the checks with SQL; developers transitioning into testing and needing to understand how databases work; and team leads and analysts who need to verify data independently without involving developers.

By the end of the course, you will confidently write SQL queries of any complexity needed for testing. You will master the structure of a typical database, learn how to find and resolve discrepancies between the UI and the database, and be able to prepare accurate queries for defect analysis on your own. You will understand how to interpret query results and use them to make decisions about product quality. The acquired knowledge will become a foundation for further growth in test automation and working with big data.