A collection of keys

select *
from   keys;

TYPE      DESCRIPTION
--------- -----------------------------------
Primary   The premier way to locate a row
Foreign   Xenophilic links to other tables
Candidate Wished it could be primary, but had
          to settle for uniqueness
Whis      The amber nectar that keeps me sane
A database without any of the first three constraints 
causes me to pour a large glass of the fourth!