Master SQL for Database Testing

1. SQL Basics

• SELECT, WHERE, ORDER BY

• DISTINCT, LIMIT, BETWEEN

• NULL handling
  
  

2. Joins

• INNER JOIN vs LEFT JOIN

• RIGHT JOIN & FULL OUTER JOIN

• Self Joins and Cross Joins
  
  

3. Aggregations

• COUNT, SUM, AVG, MIN, MAX

• GROUP BY & HAVING

• Use cases in reporting/test validations
  
  

4. Subqueries & Nested SELECTs

• Scalar vs Correlated Subqueries

• IN, EXISTS, and NOT EXISTS usage

• Real-life test scenarios
  
  

5. Set Operations

• UNION vs UNION ALL

• INTERSECT & EXCEPT (if supported)

• Common use in data comparison
  
  

6. Data Manipulation

• INSERT, UPDATE, DELETE

• Bulk operations

• Transactions & rollbacks in test setup
  
  

7. Data Validation Techniques

• Writing queries for test assertions

• Comparing expected vs actual data

• Working with audit/history tables
  
  

8. Indexes & Performance Tips

• When indexes matter for tests

• Avoiding slow queries in CI pipelines

• Explain plans & query optimization basics
  
  

9. Common SQL Interview Questions

• Query for nth highest salary

• Find duplicates in a table

• Identify orphan records via JOINs
  
  

10. SQL + Automation Integration

• JDBC (Java), PyODBC (Python)

• Using SQL in Postman/SOAP UI test scripts

• Framework integration (Selenium, TestNG, Pytest)