In the provided PHP code, what improvements could be made to enhance the security and efficiency of handling user input and database operations?

The provided PHP code is vulnerable to SQL injection attacks due to the direct concatenation of user input into SQL queries. To enhance security and efficiency, we should use prepared statements with parameterized queries to prevent SQL injection attacks and improve performance by reusing query execution plans. Additionally, we should validate and sanitize user input to prevent other types of attacks and ensure data integrity. 

// Improving security and efficiency of handling user input and database operations

// Establish a database connection
$pdo = new PDO("mysql:host=localhost;dbname=mydatabase", "username", "password");

// Prepare a SQL statement with a parameterized query
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username");

// Bind the user input to the prepared statement
$stmt->bindParam(':username', $_POST['username']);

// Execute the prepared statement
$stmt->execute();

// Fetch the results
$results = $stmt->fetchAll(PDO::FETCH_ASSOC);

// Sanitize and validate user input
$username = filter_var($_POST['username'], FILTER_SANITIZE_STRING);

// Use the sanitized input in the query
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username");
$stmt->bindParam(':username', $username);
$stmt->execute();
$results = $stmt->fetchAll(PDO::FETCH_ASSOC);

Keywords

SQL injection prepared statements password hashing input validation PDO.

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