Well, my goal is to find a primary key for the hit data.  I need to be able to identify each row uniquely.  Just a user id won't be enough.  Matching to do a join to my other datasets won't be a problem.  But, I need a PK in the table for optimization.

I am working to bring in our Clickstream data into a local database for deeper analysis correlated with internal data.  Is there a recommended combination of columns to be used as a primary key?  I assume it would be post_visid_high, post_visid_low and one of the time based columns like post_t_time_...