Database conditions allow alternate paths of control depending on the
  truth value of a test involving conditions peculiar to the database
  environment.  The database conditions are the tenancy, member, and
  database key conditions.

  The database key condition determines whether: (1) two database key
  values identify the same database record, (2) a database key value
  is null, or (3) a database key value is identical to any database
  key value in a keeplist.

  Format -

                           { ALSO database-key    }
   database-key IS [ NOT ] { NULL                 }
                           { WITHIN keeplist-name }

  database-key
   references a currency indicator or a keeplist entry in the
   Sub-Schema Section.