Convert WordPress database to utf8mb4

utf8mb4-convert.php

<?php
/*
Plugin Name: utf8mb4-convert
Version: 1.0
*/

function update_db_to_utf8mb4()
{
	set_time_limit(MINUTE_IN_SECONDS * 30);

	if (!isset($_GET['update-utf8mb4'])) {
		return;
	}

	require_once ABSPATH . 'wp-admin/includes/upgrade.php';
	require_once ABSPATH . 'wp-admin/includes/admin.php';
	require_once ABSPATH . 'wp-admin/includes/schema.php';

	global $wpdb;

	if (is_multisite()) {
		$tables = $wpdb->tables('blog');
	} else {
		$tables = $wpdb->tables('all');

		if (!wp_should_upgrade_global_tables()) {
			$global_tables = $wpdb->tables('global');
			$tables = array_diff_assoc($tables, $global_tables);
		}
	}

	foreach ($tables as $table) {
		maybe_convert_table_to_utf8mb4($table);
	}

	$wpdb->query("ALTER DATABASE {$wpdb->dbname} CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;");

	$tables = $wpdb->get_results("
SELECT table_name, engine
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA='{$wpdb->dbname}'
AND TABLE_COLLATION!='utf8mb4_unicode_ci'
AND TABLE_TYPE='BASE TABLE';
");

	foreach ($tables as $table) {
		if (preg_match('/^wp_(spbc|cleantalk)/', $table->table_name)) {
			continue;
		}

		$wpdb->query("ALTER TABLE $table->table_name ENGINE = InnoDB;");
		$wpdb->query("ALTER TABLE $table->table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;");
	}

	echo 'DB converted to utf8mb4';
	die;
}

add_action('wp_loaded', 'update_db_to_utf8mb4');