currently the following is working:
1. $describe table;
2. $describe table.column;
while, these are not working:
3. $describe column;
4. $describe database.table;
5. $describe database.table.column;
always errors about the starting element is not a valid Table.
Hive should support #3 and #5, since these are standard syntax, by updating Hive.g and related parser/lexer.
For #4, a new configuration property may be needed to distinguish #2 with #4.
Or, shall we always try matching both #2 and #4 when doing parsing? And error out if and only if neither matches? In this way, no new configuration property needed.
This is also related to HIVE-2228.