docs: function numberOfRows(node, context, callback) {
      var sql = exactCountTemplate({
          sourceQuery: node.sql()
      });
      context.runSQL(sql, function(err, resultSet){
          var counted_rows = null;
          if (!err) {
              counted_rows = resultSet.rows[0].result_rows;
          }
          return callback(err, counted_rows);
      });
  }