Select max from multiple tables using angularjs and sqlite

I have a table called "clientes" and another one called "phones", both of them have a column "_modificado" which have a timestamp, I use a function to get the last modified item to compare with my api and then update it.

how can I use the same function to retrieve the results of the 2 tables?

  function getLastSyncClientes(param) {
            db.transaction(
                function (tx) {
                    var sql = "SELECT MAX(_modificado) as lastS FROM clientes";

                    tx.executeSql(sql, [],
                        function (tx, results) {

                            var lastSync = results.rows.item(0).lastS;
                            param(lastSync);
                            log('Last local timestamp is ' + lastSync);

                        }
                    );

                },
                txErrorHandler,
                function () {

                }
            );
        }