docs: function estimatedNumberOfRows(node, context, callback) {
      var sql = estimatedCountTemplate({
          sourceQuery: node.sql()
      });
      context.runSQL(sql, function(err, resultSet){
          var estimated_rows = null;
          if (!err) {
              if (resultSet.rows) {
                  estimated_rows = resultSet.rows[0]['QUERY PLAN'][0].Plan['Plan Rows'];
              } else {
                  // If we get no results (e.g. working with a fake db)
                  // we make a most permissive estimate
                  estimated_rows = 0;
              }
          }
          return callback(err, estimated_rows);
      });
  }