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SQL Injection

Prevent SQL injection with parameterized queries and ORM.

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SQL Injection

What Is SQL Injection?

// VULNERABLE
String query = "SELECT * FROM users WHERE name = '" + input + "'";
// Input: ' OR '1'='1
// Result: SELECT * FROM users WHERE name = '' OR '1'='1'
// Returns ALL users!

Prevention

// SAFE - PreparedStatement
PreparedStatement stmt = conn.prepareStatement(
    "SELECT * FROM users WHERE name = ?");
stmt.setString(1, input);

SQL Injection Signs

  • Unexpected data in responses
  • Database errors in responses
  • Authentication bypass
  • Data exfiltration

SQL Best Practices

Query Writing

  • Use parameterized queries
  • Avoid N+1 queries
  • Use appropriate JOIN types
  • Limit result sets

Performance

  • Use EXPLAIN for analysis
  • Optimize subqueries to JOINs
  • Use temporary tables for complex queries
  • Implement proper pagination

Security

  • Never concatenate user input
  • Use stored procedures for complex logic
  • Implement query timeouts
  • Log slow queries

Key Points

  • Understanding SQL Injection is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0/3solved
Implement SQL Injection

Design and implement a solution for SQL Injection in a backend system. Consider scalability, error handling, and production readiness.

Solution
// SQL Injection implementation
// Key aspects: validation, error handling, logging, testing

public class SQLInjection {
    // Production-ready implementation
}
SQL Injection Edge Cases

Identify and handle edge cases for SQL Injection. What happens under high load, with invalid input, or during failures?

Solution
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
SQL Injection Testing Strategy

Write a testing strategy for SQL Injection. Include unit tests, integration tests, and performance tests.

Solution
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. How to prevent SQL injection?

Question 1 options

2. SQL injection input example?

Question 2 options

3. What is the primary purpose of SQL Injection?

Question 3 options

4. What is a common mistake when implementing SQL Injection?

Question 4 options

Flashcards

Question

Prevent SQL injection?

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Answer

PreparedStatement with bind variables

Question

SQL injection sign?

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Answer

Unexpected data, auth bypass, DB errors in response

Question

What is SQL Injection?

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Answer

SQL Injection is a key concept in backend development.

Question

When to use SQL Injection?

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Answer

Use SQL Injection when building production systems that require reliability, scalability, and maintainability.

Question

SQL Injection best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1.SQL injection inserts malicious SQL
  • 2.Use PreparedStatement to prevent
  • 3.Never concatenate user input into SQL
  • 4.Input validation is additional defense

Interview Tips

  • •Know SQL injection prevention
  • •Identify injection vulnerabilities

Cheat Sheet

SQL Injection

  • Malicious SQL in user input
  • Prevent: PreparedStatement
  • Never: concatenate input into SQL
  • Signs: unexpected data, auth bypass