Database, SQL, PDO, and WordPress wpdb

WordPress Data API Preference

Need	Prefer
Query posts	WP_Query, get_posts()
Post fields	get_post(), template tags
Post meta	get_post_meta(), update_post_meta()
User meta	get_user_meta(), update_user_meta()
Term meta	get_term_meta(), update_term_meta()
Site settings	get_option(), update_option()
Temporary cache	get_transient(), set_transient()
Custom SQL	$wpdb

WP_Query and get_posts

$query = new WP_Query([
    'post_type'      => 'book',
    'post_status'    => 'publish',
    'posts_per_page' => 10,
]);

$ids = get_posts([
    'post_type'      => 'book',
    'fields'         => 'ids',
    'posts_per_page' => 20,
]);

Use wp_reset_postdata() after secondary loops.

Meta and Options

$value = get_post_meta($post_id, '_book_isbn', true);
update_post_meta($post_id, '_book_isbn', $isbn);
delete_post_meta($post_id, '_book_isbn');

$settings = get_option('myplugin_settings', []);
update_option('myplugin_settings', $settings, false);
delete_option('myplugin_settings');

Avoid autoloading large option data.

Transients

$items = get_transient('myplugin_items');

if (false === $items) {
    $items = myplugin_fetch_items();
    set_transient('myplugin_items', $items, 10 * MINUTE_IN_SECONDS);
}

wpdb Basics

global $wpdb;

$table = $wpdb->prefix . 'myplugin_logs';

Prepared Select

$row = $wpdb->get_row(
    $wpdb->prepare(
        "SELECT * FROM {$table} WHERE id = %d",
        $id
    ),
    ARRAY_A
);

get_var, get_row, get_results

$count = $wpdb->get_var("SELECT COUNT(*) FROM {$wpdb->posts}");
$row = $wpdb->get_row($sql, ARRAY_A);
$rows = $wpdb->get_results($sql, ARRAY_A);

Insert, Update, Delete

$wpdb->insert(
    $table,
    ['user_id' => $user_id, 'event_name' => $event_name],
    ['%d', '%s']
);

$wpdb->update(
    $table,
    ['event_name' => $event_name],
    ['id' => $id],
    ['%s'],
    ['%d']
);

$wpdb->delete($table, ['id' => $id], ['%d']);

prepare Placeholders

Placeholder	Type
%s	String
%d	Integer
%f	Float
%i	Identifier in supported WordPress versions

Custom Tables and dbDelta

require_once ABSPATH . 'wp-admin/includes/upgrade.php';
dbDelta($sql);

PDO Outside WordPress

$pdo = new PDO($dsn, $user, $password, [
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
]);

$stmt = $pdo->prepare('SELECT * FROM users WHERE email = :email');
$stmt->execute(['email' => $email]);
$row = $stmt->fetch(PDO::FETCH_ASSOC);

Inside WordPress, use $wpdb unless there is a strong reason not to.

Performance Notes

• Request only needed fields.
• Avoid slow meta queries on large sites.
• Add indexes for custom tables based on real query patterns.
• Cache expensive computed values.
• Avoid running write queries on every page load.
• Use Query Monitor during development.

Common Pitfalls

• Using raw SQL when WP_Query is enough.
• Forgetting $wpdb->prepare().
• Using post meta for high-volume relational data.
• Creating custom tables without schema versioning.
• Storing large autoloaded options.
• Forgetting multisite prefixes.