code: function runQuery(client, queryString, args, callback) {
    if (activeBackend === 'mysql') {
      queryString = queryString.replace(/\$\d+/, '?');
    }
  
    client.query(queryString, args, function (err, result) {
      if (err) {
        callback(err, null);
        return;
      }
      if (activeBackend === 'mysql') {
        callback(err, result);
      }
      else if (activeBackend === 'pgsql') {
        var rows = [];
        if (result.rows) {
          rows = result.rows;
        }
        callback(err, rows);
      }
    });
  }
docs: Do the actual work of running the query.