SQL and Database Testing
Foundational skill (2015-2025). See the master guide for context.
The UI shows what the user sees. The API shows what the application exchanges. The database shows what actually happened. A QA engineer who can query the database directly verifies truth at the source — confirming that data was written correctly, constraints were enforced, and referential integrity was maintained, regardless of what the UI displayed.
Topics Covered
1. SQL Essentials — 01-sql-essentials/
- SELECT Queries — verification queries, using SQL in test automation, and common patterns
- JOINs and Aggregation — JOIN types, GROUP BY, HAVING, and investigation queries
- Data Manipulation — INSERT, UPDATE, DELETE for test data, transactions, and safe practices
2. Database Testing — 02-database-testing/
- Constraint Testing — primary keys, foreign keys, unique constraints, NOT NULL, and CHECK constraints
- Migration Testing — schema migrations, rollback verification, data preservation, and performance
- Stored Procedures — testing business logic in the database, triggers, and computed values
3. Beyond SQL — 03-beyond-sql/
- NoSQL Basics — MongoDB, Redis, DynamoDB testing patterns
- Data Masking — anonymization, compliance testing, and interview talking points
Why This Matters
SQL is the verification layer that sits beneath every API and UI test. When an API call creates a record, a database query confirms it was persisted correctly. When a bug report says "data is missing," SQL finds the truth. Database testing skills make every other form of testing more reliable.