title: Calculate date and time key in fact table using existing date time field
body: <p>I have date time field in a fact table in the format MM/DD/YY HH:MM:SS (e.g 2/24/2009 11:18:47 AM) and I have seperate date and time dimension 
  tables. What I would like ask is that how I can create date key and time key in the fact table using the date time field so that I can join the
  date and time dimension.</p>
  
  <p>There are alot of reference for creating seperate date and time dimension and their benefit but I could not find how to create date and time keys
  in the fact table using existing date time field.</p>
  
  <p>I have also heard that having date time field in fact table has certain benefit. If so, what would you recommend, should I have all three (date key, time key
  and date time field) in the fact table. Date key and time key are must to have for me and I am concerned about fact table size if I have date time field
  also in the fact table.</p>
  
  <p>Thank you all for any help you can give.</p>