Unable to query custom data object using SQL

Summary:

We have two custom objects in Fusion CX Sales, both of them are custom top level objects. However, when I try to pull these two custom object data through creating dataset in OTBI, the dataset returns no data. The SQL query that I have as a first trial is:
select * from mkt_ref_entities, when that didn't work, I tried select * from zca_ref_entities.

Usually these two data tables store the custom objects/child custom objects, but this time I cannot query any data out of it. Is there any processes that I need to run to make these two custom objects available in the dataset area in OTBI?