How can PHP be used to query a SQL database and compare values to trigger actions based on specific criteria?

To query a SQL database and compare values to trigger actions based on specific criteria, you can use PHP's PDO (PHP Data Objects) extension to connect to the database and execute SQL queries. You can fetch the results from the database and then use conditional statements in PHP to compare the values and trigger actions accordingly.

<?php
// Connect to the database
$pdo = new PDO('mysql:host=localhost;dbname=mydatabase', 'username', 'password');

// Prepare and execute a SQL query
$stmt = $pdo->prepare('SELECT * FROM mytable WHERE column = :value');
$stmt->execute(['value' => $criteria]);

// Fetch the results
$results = $stmt->fetchAll();

// Compare values and trigger actions
foreach ($results as $row) {
    if ($row['column'] == $criteria) {
        // Perform action
    }
}
?>