Custom SQL query in BVC-Oracle

I wanted to know whether we can run complex queries using the field "Custom SQL query" in BVC-Oracle.

So far I know that we can run queries like - select "columnName" from "Table"

and then add a Field by the name which matches the "columnName"

In other words - what are the limitations to running a Custom SQL query in BVC-Oracle?

BTW I am on CCS 10.5.

Thanks,

Chaitali