Support ordinal in GROUP/ORDER BY clause

[dai-chen]

In issue #213, it seems BI tool like Tableau will generates GROUP BY (and probably ORDER BY too) using ordinal.

Take query SELECT age FROM accounts GROUP BY 1 for example, the ordinal 1 here is referring to field age. So actually this query is Equivalent to SELECT age FROM accounts GROUP BY age. Although it's said this is not a good practice, we need to support this for integration with BI tool.

Reference:

1. https://stackoverflow.com/questions/7392730/what-does-sql-clause-group-by-1-mean
2. https://dba.stackexchange.com/questions/86609/why-do-we-use-group-by-1-and-group-by-1-2-3-in-sql-query

[abbashus]

Fixed by #248.