You have run and tested your Oracle query in your fave client, such as Oracle SQL Developer or Toad. The query tests fine and returns a bunch of rows. You create an Oracle connection (see https://msdn.microsoft.com/en-us/library/gg399158%28v=sql.110%29.aspx), you paste your tested Oracle SQL query into the PowerPivot query window, the query validates ok, but when you run the query in PowerPivot, 0 rows are returned.
Chances are you could be using a date expression in your query that works a little differently through PowerPivot.
Instead of …
WHERE YourDate = ’11/APR/2015′
WHERE YourDate = ‘2015-04-11’