Position 21 specifies the sequence of input fields used with the match fields specification (positions 65 and 66 of the input specifications). Position 21 applies only to input, update, or combined files used as primary or secondary files. Use positions 65 and 66 of the input specifications to identify the fields containing the sequence information.
If more than one input file with match fields is specified in the program, a sequence entry in position 21 can be used to check the sequence of the match fields and to process the file using the matching record technique. The sequence need only be specified for the first file with match fields specified. If sequence is specified for other files, the sequence specified must be the same; otherwise, the sequence specified for the first file is assumed.
If only one input file with match fields is specified in the program, a sequence entry in position 21 can be used to check fields of that file to ensure that the file is in sequence. By entering one of the codes M1 through M9 in positions 65 and 66 of the input specifications, and by entering an A, blank, or D in position 21, you specify sequence checking of these fields.
Sequence checking is required when match fields are used in the records from the file. When a record from a matching input file is found to be out of sequence, the RPG IV exception/error handling routine is given control.