Oracle Refresh very slow

[ACol123]

Hi guys, I'm working on a project with Oracle data source.

In Power BI the DB contains 40.5 million rows and the refresh takes about 15 hours (only table without merge).

Same project in Tableau with same query completes refresh in 50 minutes.

Can you tell me how this is possible?

Thanks in advance

[ACol123]

Hi, I'm working on native driver. 

In the query I'm going to remove some columns that I don't need from the database, but I think it's a simple query. I'm not using merge.

[lbendlin]

How long does it take with Toad?

[lbendlin · Accepted solution]

native driver or ODBC?  Complex query or simple table spool?  Are you attempting any merges?