You can get the Max Date by simplying adding a MAX( [date] ) field to the Database source. However, I do not believe it is possible to get the corresponding Interesting_attribute. It would require a table calculation on the secondary data source, which would then need to be blended in. To my knowledge, this is not how blending works. I present you with 2 alternatives:
1) Add the [date] field to "Selected List" with a value of the maximum date from the Database
2) Add a flag to "Database" that takes a value of 1 if and only if [date] is the maximum date for that company.
Hope this helps,