Create database table upon plugin activation

create-database-table-after-plugin-activated.php

<?php
register_activation_hook( __FILE__, array( 'SAMPLE_CLASS', 'plugin_activated' ) );
class SAMPLE_CLASS {
  public function plugin_activated() {
    $add_custom_table = $wpdb->prefix . 'table_name';
    if($wpdb->get_var("SHOW TABLES LIKE '$add_custom_table'") != $add_custom_table) {
        $charset_collate = $wpdb->get_charset_collate();
        $sql = "CREATE TABLE IF NOT EXISTS $add_custom_table (
                        `id` int(100) NOT NULL auto_increment,
                        `field_label` int(100) NOT NULL,
                        `field_name` VARCHAR(255) NOT NULL,
                        UNIQUE KEY `id` (`id`)
                        ) $charset_collate;";
        require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
        dbDelta($sql);
    }
  }
}