Declares and opens a record stream. The undeclared START_STREAM
    statement:

    o  Forms a record stream from one or more relations. The record
       selection expression determines the records in the record
       stream.

    o  Places a pointer for that stream just before the first record
       in this stream.

    You must then use the FETCH statement to advance the pointer one
    record at a time through the stream and other RDML statements
    (for example, MODIFY and ERASE) to manipulate each record.