Understanding PHP Database Extension Requirements

Understanding PHP Database Extension Requirements

Different PHP frameworks and CMSs have specific database extension requirements. Installing pdo_mysql doesn’t automatically give you access to the legacy mysql or mysqli extensions — they’re separate modules.

Check What’s Installed

php -m | grep -i mysql
# Output might show:
pdo_mysql
mysqlnd

Verify Specific Extension Availability

<?php
if (extension_loaded('pdo')) {
    echo "PDO: Available\n";
}

if (extension_loaded('mysqli')) {
    echo "MySQLi: Available\n";
} else {
    echo "MySQLi: MISSING\n";
}

The Legacy Trap

Many legacy applications explicitly check for mysqli or mysql functions, even if PDO is available. When migrating to Docker or upgrading PHP versions, audit your Dockerfile’s docker-php-ext-install list against your framework’s actual requirements, not assumptions.

Example: Some CMS platforms check function_exists('mysqli_connect') during installation, which fails if only pdo_mysql is present.

The Fix

# Add to your Dockerfile
RUN docker-php-ext-install \
    pdo_mysql \
    mysqli \
    # ...other extensions

Don’t assume one database extension covers all use cases. Check the framework’s documentation and test explicitly.