Hi Sangeetha -
As you've likely discovered,Tableau Desktop will used local, aggregated/cached results whenever possible to cut down on round-trips to the data source. The tool doesn't implement "listeners" to allow a data source to alert it that "new" data has arrived. As a result, you'll need to manually refresh your report/dashboard if you've previously asked the "same question" (and Tableau therefore has cached the necessary rows to answer that question).
If you have access to Tableau Server and are displaying results there, you can use the Server's cache settings and/or a special :refresh=y parameter to always show latest/greatest results. However, this won't help you in Desktop-only land.
Thanks alot for the reply...