Column <str> is used in a primary or unique key but permits NULL
  values

  Explanation:  You specified a column in a primary or unique key
  definition which permits NULL values.  The current ANSI and ISO
  SQL standards require that only fields for which NOT NULL is
  specified may be included in a primary or unique key.

  User Action:  If it is important to have only standard syntax in
  your program, you should either remove the column from the
  primary or unique key, or add the NOT NULL attribute to the
  column.