public static function v110() {
        global $wpdb;

        $db = DB_NAME;
        $cst = self::getComboSetsTable();

        // drop wp_usces_item post ID foreign key
        $foreignKeyExists = (bool)(int)$wpdb->get_var("SELECT COUNT(*)
            FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
            WHERE
                CONSTRAINT_SCHEMA = '{$db}' AND
                TABLE_NAME        = '{$cst}' AND
                CONSTRAINT_NAME   = '{$cst}_ibfk_1' AND
                CONSTRAINT_TYPE   = 'FOREIGN KEY'
        ");
        if ($foreignKeyExists === true) {
            $wpdb->query("ALTER TABLE {$cst} DROP FOREIGN KEY `{$cst}_ibfk_1`");
        }

        // drop wp_usces_skus meta ID foreign key
        $foreignKeyExists = (bool)(int)$wpdb->get_var("SELECT COUNT(*)
            FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
            WHERE
                CONSTRAINT_SCHEMA = '{$db}' AND
                TABLE_NAME        = '{$cst}' AND
                CONSTRAINT_NAME   = '{$cst}_ibfk_2' AND
                CONSTRAINT_TYPE   = 'FOREIGN KEY'
        ");
        if ($foreignKeyExists === true) {
            $wpdb->query("ALTER TABLE {$cst} DROP FOREIGN KEY `{$cst}_ibfk_2`");
        }
    }