Re: Definition Needed: "proper superkey"
Date: Mon, 4 Aug 2008 14:10:55 -0700 (PDT)
>> I can not find a definition for "proper superkey". I have found "superkey", but not "proper superkey". <<
I never heard that one either. So, I will make a wild guess :)
Some superkeys are keys with extra columns tacked on the end which can be tirmmed -- (vin, assigned_parking_space). You might use it to get a covering index.
Some superkeys have several subsets which are candidate keys -- given Schedule (teacher, room_nbr, class_period), we could make all three columns into the key, but (room_nbr, class_period) -> teacher and (teacher, class_period) -> room_nbr which gives us other, smaller keys and no rule for picking which one to use.
Maybe a "proper superkey" is one of these situations? Received on Mon Aug 04 2008 - 23:10:55 CEST