Assigns values from data records in a record stream to host
    variables in RDML programs. You can use the GET statement in
    three different ways:

    o  When you establish a record stream with the FOR or
       START_STREAM statement, you use the GET statement to assign
       values from the current record in the stream to variables in
       your program. In the case of the START_STREAM statement, you
       also need a FETCH statement to indicate the current record in
       the stream.

    o  You can use GET within a STORE operation to retrieve the value
       of the record currently being stored. This includes the use of
       GET ... RDB$DB_KEY in a STORE ... END_STORE block to retrieve
       the database key (dbkey) of a record just stored.

    o  You can also use the GET statement alone, without a FOR,
       FETCH, or STORE statement to retrieve the result of a
       statistical expression. The record stream is formed by the
       record selection expression within the statistical expression.