SQL has order by, there will be one more column(the sort column) in result plan

[JiaTao Tao]

SQL;
```
SELECT u.ID, u.NAME
FROM USERS u
ORDER BY u.AGE
```

PLAN:
```
LogicalSort(sort0=[$2], dir0=[ASC])
  LogicalProject(ID=[$0], NAME=[$1], AGE=[$2])
    EnumerableTableScan(table=[[RECR, USERS]])
```
Plan's row type: RecordType(INTEGER ID, VARCHAR NAME, INTEGER AGE)

But the SQL only project ID and NAME, there should be a LogicalProject
(ID, NAME) on LogicalSort. Is this by design? And what about this extra
column?



Regards!

Aron Tao