How does caching variables differ from caching database queries in PHP?

Caching variables involves storing the value of a variable in memory for quick retrieval, while caching database queries involves storing the results of a database query in memory to avoid repeated querying of the database. Caching variables is typically used for storing values that are computationally expensive to calculate or frequently used, while caching database queries is used to improve the performance of applications that make frequent database calls. 

// Caching variables
$expensiveCalculation = null;

function getExpensiveCalculation() {
    global $expensiveCalculation;
    
    if ($expensiveCalculation === null) {
        // Perform expensive calculation
        $expensiveCalculation = 10 * 5;
    }
    
    return $expensiveCalculation;
}
echo getExpensiveCalculation(); // Output: 50

// Caching database queries
$pdo = new PDO("mysql:host=localhost;dbname=test", "username", "password");
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

function getCachedData() {
    global $pdo;
    
    $stmt = $pdo->query("SELECT * FROM table WHERE condition");
    $result = $stmt->fetchAll(PDO::FETCH_ASSOC);
    
    return $result;
}
$data = getCachedData();

Keywords

caching variables database queries PHP differences

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