A compression clause for all-numeric fields that translates
    the field values into a more compactly encoded form. You can
    mix mapped and unmapped fields, but the most storage space is
    gained by building indexes of multiple fields of data type WORD
    or LONGWORD. Oracle Rdb attempts to pack all such fields into the
    smallest possible space.

    The "lo-val" (low value) through "hi-val" (high value) parameters
    specify the range of integers as the value of the index key.

    The valid range of the compressed key:

    o  Cannot be zero

    o  The range "high-val" through "low-val" is limited to (2**31) -
       4 x (10**scale)

       If the value of the key is less than zero or greater than

       (2**31) - 4 x (10**scale), Oracle Rdb signals an exception.

    The following notes refer to compressed indexes:

    All text compressed indexes require the DUPLICATES ARE ALLOWED
    clause, which is the default for the DEFINE INDEX statement. If
    the SIZE IS clause is specified, the field referred to by the
    clause must be of the TEXT or VARYING TEXT data type. The field
    must also be the same length or greater in length than the value
    specified in the SIZE IS clause.

    For integer field compressed indexes, the index field must be
    of data type WORD or LONGWORD. You can mix mapped and unmapped
    fields, but the most storage space is gained by building indexes
    of multiple fields of data type WORD or LONGWORD. Oracle Rdb
    attempts to pack all such fields into the smallest possible
    space.

    Compressed key suffixes also enable the user to use fields longer
    than 254 characters as index keys.

    If any data values already stored are less than "lo-val" or
    greater than "hi-val", the DEFINE INDEX statement will fail.

    A subsequent STORE or MODIFY operation that attempts to store a
    value less than "lo-val" or greater than "hi-val" will fail.