Hello there Karthick,
Hope you're doing well.
When you use a Group By clause in an SQL statement, you have to include the attribute from the Group By in the Select.
Also, this clause is used alongside with the aggregate function that you want to use (for example Count, Max, Min, Sum, Avg).
As an example, if you want to count the different rooms with the same price, you may do something like:
Select {Room}.Price, Count(1)
From {Room}
Group By {Room}.Price
The SQL statement depends on what you want to achieve.
Hope that this helps you!
Kind regards,
Rui Barradas