PHP Prepared Statements
Prepared statements are very useful against SQL injections.
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:
- 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(?, ?, ?)
- The database parses, compiles, and performs query optimization on
the SQL statement template, and stores the result without executing it
- 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.
Prepared Statements in MySQLi
The following example uses prepared statements and bound parameters in MySQLi:
Example (MySQLi with Prepared Statements)
<?php
$servername = "localhost";
$username = "username";
$password =
"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 (firstname, lastname, email) 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", $firstname, $lastname, $email);
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
- d - double
- s -
string
- b - BLOB
We must have one of these for each parameter.
By telling mysql what type of data to expect, we minimize the risk of SQL injections.
|
Note: If we want to insert any data from external sources
(like user input), it is very important that the data is sanitized and validated. |
Prepared Statements in PDO
The following example uses prepared statements and bound parameters in 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 MyGuests (firstname, lastname, email)
VALUES (:firstname, :lastname, :email)");
$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;
?>
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