PHP MySQL Prepared Statements
PHP MySQL Prepared Statements
PHP MySQL prepared statements are mainly used to prevent SQL injection attacks and to improve performance.
Prepared statements seperates the data from SQL commands.
Prepared statements basically work like this:
- Prepare: An SQL query template with placeholders is sent to the server. The data values are not sent. Example: INSERT INTO MyGuests VALUES(?, ?, ?). Then, the server parses, compiles, and optimizes the SQL query template, without executing it
- Execute: At a later time, the application binds the values to the parameters, and the database executes the query. The application may execute the query as many times as it wants with different values
Prepared statements have four main advantages:
- Reduced parsing time - as the preparation on the query is done only once (although the statement is executed multiple times)
- Minimize bandwidth - Bound parameters minimize bandwidth to the server as you need send only the parameters each time, and not the whole query
- Security - 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
- Cleaner code - by seperating data from SQL commands
Prepared Statements in MySQLi
The following example uses prepared statements 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 the SQL query template
$stmt = $conn->prepare("INSERT INTO MyGuests (firstname, lastname, email) VALUES (?, ?, ?)");
// Bind parameters
$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 in PDO:
Example - PDO with Prepared Statements
<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
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 the SQL query template
$stmt = $conn->prepare("INSERT INTO MyGuests (firstname, lastname, email") VALUES (?,
?, ?);
// Execute with values
$stmt->execute(['John', 'Doe', 'john@example.com']);
$stmt->execute(['Mary', 'Moe', 'mary@example.com']);
$stmt->execute(['Julie', 'Dooley', 'julie@example.com']);
echo "New records created successfully";
} catch(PDOException $e)
{
echo "Error: " . $e->getMessage();
}
$conn = null;
?>
