What are some common mistakes to avoid when writing PHP code for form validation and database queries?

One common mistake to avoid when writing PHP code for form validation is not properly sanitizing user input, which can lead to SQL injection attacks. To solve this issue, use prepared statements with parameterized queries to prevent malicious input from affecting your database queries. 

// Example of using prepared statements for database queries
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username");
$stmt->bindParam(':username', $username);
$stmt->execute();
```

Another common mistake is not validating user input before processing it, which can lead to unexpected behavior or security vulnerabilities. To solve this issue, always validate and sanitize user input before using it in your code.

```php
// Example of validating user input before processing
$email = $_POST['email'];

if(filter_var($email, FILTER_VALIDATE_EMAIL)) {
    // Process the email
} else {
    // Handle invalid email input
}

Keywords

SQL injection XSS attacks prepared statements input validation error handling

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