Check If a Row Exists in PDO

At times, you may need to check if a row exists to avoid duplication when inserting or to prevent issues related to similar data in the records. PHP PDO allows you to perform this task securely.

So PDO (PHP Data Objects) is a database abstraction layer in PHP that allows you to interact with databases securely. It supports multiple database systems and makes it easy to write SQL queries with prepared statements, which help prevent SQL injection.

Anyway, lets see how we can do that step by step.

Establish Database Connection

First, let’s connect PHP to the database. Here is an example:

try {
    $pdo = new PDO('mysql:host=localhost;dbname=your_database_name', 'database_username', 'database_password');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $err) {
    die("Database connection failed: " . $err->getMessage());
}

This will display an error message if the connection fails or if the database credentials provided are incorrect.

Anyway, let’s move on to the following section to understand how to build the SQL query for selecting records to check if rows exist.

Write the SQL Query

Once you have ensured the connection is successful, you can build the SQL query using the following code:

SELECT COUNT(*) FROM your_table WHERE column_name = :value

The goal is to use this query in PHP to check if a row exists. Let’s see how to implement this in PHP and prepared statement.

Use a Prepared Statement to Execute the Query

Prepared statements make your code more secure by binding parameters. Here is how you can do that:

$sql = "SELECT COUNT(*) FROM users WHERE email = :email";
$stmt = $pdo->prepare($sql);
$stmt->execute(['email' => '[email protected]']);
$count = $stmt->fetchColumn();

if ($count > 0) {
    echo "The row exists.";
} else {
    echo "The row does not exist.";
}

The :email placeholder will be replaced with the actual value, protecting your application from SQL injection attacks.

You can also do the same task with using LIMIT keyword to improve performance when working with large tables:

$sql = "SELECT 1 FROM users WHERE email = :email LIMIT 1";
$stmt = $pdo->prepare($sql);
$stmt->execute(['email' => '[email protected]']);

if ($stmt->fetch()) {
    echo "The row exists.";
} else {
    echo "The row does not exist.";
}

The search will stop as soon as it finds a matching result. Using PDO and prepared statements helps ensure that queries are secure from SQL injection attacks.

Anyway, the output would look like the following if the email already exists: 

The row exists

And if it does not exist, it would display the following notice:

The row does not exist.

Let’s take a look at the final example.

The Complete Example

// => this is the database connection
try {
    $pdo = new PDO('mysql:host=localhost;dbname=your_database_name', 'database_username', 'database_password');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $err) {
    die("Database connection failed: " . $err->getMessage());
}

// => Here is an example of using a prepared statement ( check for a record exists )
$sql = "SELECT COUNT(*) FROM users WHERE email = :email";


$stmt = $pdo->prepare($sql);
$stmt->execute(['email' => '[email protected]']);
$count = $stmt->fetchColumn();

if ($count > 0) {
    echo "The row exists.";
} else {
    echo "The row does not exist.";
}

// => Here is another example using the LIMIT keyword ( check the row exists )
$sql = "SELECT 1 FROM users WHERE email = :email LIMIT 1";
$stmt = $pdo->prepare($sql);
$stmt->execute(['email' => '[email protected]']);

if ($stmt->fetch()) {
    echo "The row exists.";
} else {
    echo "The row does not exist.";
}

Let’s summarize it.

Wrapping Up

Checking if a row exists in your database is an important task, and PDO makes it both secure and effective in preventing your application from SQL injection attacks. Here is a quick recap of what we covered in this tutorial:

• Connecting to the Database: Using the new PDO() to establish a connection and handle errors.
• Writing the Query: Using SELECT COUNT(*) or SELECT 1 to check if a row exists.
• Executing the Query: Binding values securely with prepared statements and fetching the result using fetchColumn() or fetch().
• Optimizing the Query: Using LIMIT 1 with SELECT 1 for better performance when scanning large tables.