docs: function (column, cb) {
              var ret = new Promise();
              this.__aggregateDataset()
                  .select(sql.min(this.stringToIdentifier(column)).as("v1"), sql.max(this.stringToIdentifier(column)).as("v2"))
                  .first()
                  .chain(function (r) {
                      ret.callback(r.v1, r.v2);
                  }, ret.errback);
              return ret.classic(cb).promise();
          }