When match fields are used in multi-file processing, the program selects the records for processing according to the contents of the match fields. At the beginning of the first cycle, the program reads one record from every primary/secondary input file and compares the match fields in the records. If the records are in ascending order, the program selects the record with the lowest match field. If the records are in descending order, the program selects the record with the highest match field.
When a record is selected from a file, the program reads the next record from that file. At the beginning of the next program cycle, the new record is compared with the other records in the read area that are waiting for selection, and one record is selected for processing.
Records without match fields can also be included in the files. Such records are selected for processing before records with match fields. If two or more of the records being compared have no match fields, selection of those records is determined by the priority of the files from which the records came. The priority of the files is:
When the primary file record matches one or more of the secondary records, the MR (matching record) indicator is set on. The MR indicator is on for detail time processing of a matching record through the total time that follows the record. This indicator can be used to condition calculation or output operations for the record that is selected. When one of the matching records must be selected, the selection is determined by the priority of the files from which the records came.
Figure 9 shows the logic flow of multi-file processing.
A program can be written where only one input file is defined with match fields and no other input files have match fields. The files without the match fields are then processed completely according to the previously mentioned priority of files. The file with the match fields is processed last, and sequence checking occurs for that file.