private String nextAlias() {
    String tabAlias = String.format("$hdt$_%d", derivedTableCount);
    derivedTableCount++;
    return tabAlias;
  }
Assumption:<br>
1. Project will always be child of Sort.<br>
2. In Calcite every projection in Project is uniquely named
(unambiguous) without using table qualifier (table name).<br>

@param order
         Hive Sort Node
@return Schema
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/translator/ASTConverter.java