docs: function (c) {
              var ret;
              if (isInstanceOf(c, AliasedExpression)) {
                  ret = [c.expression, c.alias];
              } else if (isString(c)) {
                  var parts = this._splitString(c), cTable = parts[0], column = parts[1], alias = parts[2];
                  if (alias) {
                      ret = [cTable ? new QualifiedIdentifier(cTable, column) : column, alias];
                  } else {
                      ret = [c, null];
                  }
              } else {
                  ret = [c, null];
              }
              return ret;
          }