Same query, Same linked server. Different result I have two instances (SQL2008R2_A and SQL2008R2_B), they have same linked server configuration to Oracle_C. I used the same query to select from Oracle_C. SQL2008R2_A returned the correct result but SQL2008R2_B get nothing.
And I tested linked server connection of both instances. They are all successfully.
Interesting...
Thank you for your response. Before post this question I already double checked the settings for both linked server and TNS name file. There is nothing different between them. 

Fortunately, I resolved it by just re-create the linked server at Server B. It might need to refresh some cache.

Thanks again and have a great one:)