Best way to prevent SQL injection in PHP?

Question

Using this:

$unsafe_variable = $_POST['user_input']; 

mysql_query("INSERT INTO table (column) 
VALUES ('" . $unsafe_variable . "')");

That's because the user can input something like

 value'); DROP TABLE table;--, and the query becomes:

INSERT INTO table (column) VALUES('`**`value');
 DROP TABLE table;--`**`')

What can be done to prevent this from happening?

Comments

Prepared statements alone won't fully prevent SQL Injection. You have to paramterize your queries too and use them both in conjunction.

Answer 1

1. Using PDO:

   $stmt = $pdo->prepare('SELECT * FROM employees WHERE name = :name');
   
   $stmt->execute(array('name' => $name));
   
   foreach ($stmt as $row) {
       // do something with $row
   }

2. Using mysqli:

   $stmt = $dbConnection->prepare('SELECT * FROM employees WHERE name = ?');
   $stmt->bind_param('s', $name);
   
   $stmt->execute();
   
   $result = $stmt->get_result();
   while ($row = $result->fetch_assoc()) {
       // do something with $row
   }

Comments

PDO with parameters does the job. Remember to protect against XSS as well.

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for prevention sql injection you can use mysql_real_escape_string ( string $unescaped_string [, resource $link_identifier = NULL ] )

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If user input is added without modification into an SQL query, then the application becomes vulnerable to SQL injection. The best way to defend this is to use prepared statements and parameterized queries. These are SQL statements that are sent to and parsed by the database server separately from any parameters making it impossible for attacker to inject malicious SQL.