Reading Multiple Rows with PDO

Iterate over database rows with fetch in a loop to control memory use.

The objective is to understand the behavior and operational limits, not only the method name.

What It Does

Iterate over database rows with fetch in a loop to control memory use.

Prerequisites

Use a dedicated development environment and sample data. Where a snippet uses an injected connection, repository, request value or mailer, supply it from your own application setup.

Example 1: Basic Use

A focused working pattern for this topic. Names such as $pdo, $authContext and $repo represent dependencies provided by the application unless initialized in the snippet.

<?php
$stmt = $pdo->prepare('SELECT id, name FROM products WHERE active = :active ORDER BY id');
$stmt->execute(['active' => 1]);
while (($row = $stmt->fetch(PDO::FETCH_ASSOC)) !== false) {
    echo htmlspecialchars($row['name'], ENT_QUOTES, 'UTF-8') . PHP_EOL;
}

Example 2: A Second Scenario

A second use case that adds a different operation or data flow specific to this topic.

<?php
$stmt = $pdo->prepare('SELECT email FROM subscribers WHERE active = ? ORDER BY id');
$stmt->execute([1]);
while (($email = $stmt->fetchColumn()) !== false) echo htmlspecialchars($email, ENT_QUOTES, 'UTF-8') . PHP_EOL;

Example 3: Practical Checks

A practical validation, failure or deployment concern specific to this topic.

<?php
$stmt = $pdo->query('SELECT id, total FROM orders ORDER BY id LIMIT 100');
$total = 0;
while (($row = $stmt->fetch(PDO::FETCH_ASSOC)) !== false) $total += (float) $row['total'];
echo $total;

Important Behavior and Edge Cases

fetchAll is convenient for small result sets but loads the complete result into PHP memory.

For production use, also account for error handling, data validation, resource limits and environment-specific driver behavior.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Iterate over database rows with fetch in a loop to control memory use.
• fetchAll is convenient for small result sets but loads the complete result into PHP memory.
• Use this workflow as a focused starting point rather than a substitute for application-level tests.

Choose this API or pattern when its exact semantics match your task, and verify the result against the database driver and runtime used by your application.