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PHP Prepared Statements


These topic helps prepared for avoid sql injection.


Prepared Statements and Bound Parameters

A prepared statement is a feature used to execute the same (or similar) SQL statements repeatedly with high efficiency.

Prepared statements basically work like this:

  1. Prepare: An SQL statement template is created and sent to the database. Certain values are left unspecified, called parameters (labeled "?"). Example: INSERT INTO MyGuests VALUES(?, ?, ?)
  2. The database parses, compiles, and performs query optimization on the SQL statement template, and stores the result without executing it
  3. Execute: At a later time, the application binds the values to the parameters, and the database executes the statement. The application may execute the statement as many times as it wants with different values

Compared to executing SQL statements directly, prepared statements have two main advantages:

  • Prepared statements reduces parsing time as the preparation on the query is done only once (although the statement is executed multiple times)
  • Bound parameters minimize bandwidth to the server as you need send only the parameters each time, and not the whole query
  • Prepared statements are very useful against SQL injections, because parameter values, which are transmitted later using a different protocol, need not be correctly escaped. If the original statement template is not derived from external input, SQL injection cannot occur.

Need for Statements in MySQLi

The following example uses prepared statements and bound parameters in MySQLi:

Example (MySQLi with Prepared Statements)

<?php
$servername = "localhost";
$name= "name";
$pass = "password";
$dbname = "myDB";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

// prepare and bind
$stmt = $conn->prepare("INSERT INTO MyGuests (firstname, lastname, email) VALUES (?, ?, ?)");
$stmt->bind_param("sss", $firstname, $lastname, $email);

// set parameters and execute
$firstname = "John";
$lastname = "Doe";
$email = "john@example.com";
$stmt->execute();

$firstname = "Mary";
$lastname = "Moe";
$email = "mary@example.com";
$stmt->execute();

$firstname = "Julie";
$lastname = "Dooley";
$email = "julie@example.com";
$stmt->execute();

echo "New records created successfully";

$stmt->close();
$conn->close();
?>

Code lines to explain from the example above:

"INSERT INTO MyGuests (name,hometown,school) VALUES (?, ?, ?)"

In our SQL, we insert a question mark (?) where we want to substitute in an integer, string, double or blob value.

Then, have a look at the bind_param() function:

$stmt->bind_param("sss", $name, $hometown, $school);

This function binds the parameters to the SQL query and tells the database what the parameters are. The "sss" argument lists the types of data that the parameters are. The s character tells mysql that the parameter is a string.

The argument may be one of four types:

  • i - integer
  • b - BLOB
  • d - double
  • s - string

We mush use of these parameter.

Mysql data can be expcted we minimize the risk of SQL injections.


Prepared Statements in PDO

Exaample of PDO:

Example (PDO with Prepared Statements)

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDBPDO";

try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    // set the PDO error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    // prepare sql and bind parameters
    $stmt = $conn->prepare("INSERT INTO Biograph (name, hometown, school)
    VALUES (:name,:hometown,:school)");
    $stmt->bindParam(':firstname', $firstname);
    $stmt->bindParam(':lastname', $lastname);
    $stmt->bindParam(':email', $email);

    // insert a row
    $firstname = "John";
    $lastname = "Doe";
    $email = "john@example.com";
    $stmt->execute();

    // insert another row
    $firstname = "Mary";
    $lastname = "Moe";
    $email = "mary@example.com";
    $stmt->execute();

    // insert another row
    $firstname = "Julie";
    $lastname = "Dooley";
    $email = "julie@example.com";
    $stmt->execute();

    echo "New records created successfully";
    }
catch(PDOException $e)
    {
    echo "Error: " . $e->getMessage();
    }
$conn = null;
?>