Cobol 1:N match sample

Here's a sample COBOL program for 1:N matching:

IDENTIFICATION DIVISION.
PROGRAM-ID. SAMPLE.

ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT MASTER-FILE ASSIGN TO "MASTER.DAT"
        ORGANIZATION IS INDEXED
        ACCESS MODE IS DYNAMIC
        RECORD KEY IS MASTER-KEY.
    SELECT TRANSACTION-FILE ASSIGN TO "TRANSACTION.DAT"
        ORGANIZATION IS LINE SEQUENTIAL.

DATA DIVISION.
FILE SECTION.
FD MASTER-FILE.
01 MASTER-RECORD.
   05 MASTER-KEY   PIC X(10).
   05 MASTER-DATA  PIC X(50).

FD TRANSACTION-FILE.
01 TRANSACTION-RECORD.
   05 TRANSACTION-KEY    PIC X(10).
   05 TRANSACTION-DATA   PIC X(50).

WORKING-STORAGE SECTION.
01 EOF-FLAG            PIC X(1) VALUE 'N'.
01 MATCH-FLAG          PIC X(1) VALUE 'N'.
01 MATCH-FOUND-FLAG    PIC X(1) VALUE 'N'.
01 ERROR-FLAG          PIC X(1) VALUE 'N'.
01 MASTER-FOUND-FLAG   PIC X(1) VALUE 'N'.
01 TRANSACTION-FOUND-FLAG  PIC X(1) VALUE 'N'.
01 MASTER-KEY-WORK     PIC X(10).
01 TRANSACTION-KEY-WORK    PIC X(10).

PROCEDURE DIVISION.
OPEN-FILES.
    OPEN MASTER-FILE.
    OPEN TRANSACTION-FILE.

PROCESS-TRANSACTION.
    READ TRANSACTION-FILE
        AT END MOVE 'Y' TO EOF-FLAG
        NOT AT END PERFORM MATCH-MASTER.

CLOSE-FILES.
    CLOSE MASTER-FILE.
    CLOSE TRANSACTION-FILE.

STOP-RUN.

MATCH-MASTER.
    MOVE TRANSACTION-KEY TO TRANSACTION-KEY-WORK.
    SET MATCH-FOUND-FLAG TO 'N'.
    SET ERROR-FLAG TO 'N'.
    SET MASTER-FOUND-FLAG TO 'N'.
    READ MASTER-FILE
        INVALID KEY SET ERROR-FLAG TO 'Y'
        NOT INVALID KEY
            PERFORM CHECK-MATCH.
    IF ERROR-FLAG = 'Y'
        MOVE 'N' TO MATCH-FOUND-FLAG.
    IF MATCH-FOUND-FLAG = 'N'
        PERFORM PROCESS-NO-MATCH.

CHECK-MATCH.
    MOVE MASTER-KEY TO MASTER-KEY-WORK.
    IF TRANSACTION-KEY-WORK = MASTER-KEY-WORK
        PERFORM PROCESS-MATCH
        SET MATCH-FOUND-FLAG TO 'Y'.
    IF MASTER-FOUND-FLAG = 'N'
        SET MASTER-FOUND-FLAG TO 'Y'.

PROCESS-MATCH.
    SET MATCH-FOUND-FLAG TO 'Y'.
    SET MASTER-FOUND-FLAG TO 'Y'.
    MOVE 'Y' TO TRANSACTION-FOUND-FLAG.
    DISPLAY "Match found for key: " MASTER-KEY.
    DISPLAY "Master data: " MASTER-DATA.
    DISPLAY "Transaction data: " TRANSACTION-DATA.

PROCESS-NO-MATCH.
    SET MATCH-FOUND-FLAG TO 'N'.
    MOVE 'N' TO TRANSACTION-FOUND-FLAG.
    DISPLAY "No match found for key: " TRANSACTION-KEY.
    DISPLAY "Transaction data: " TRANSACTION-DATA.

In this program, the `MASTER-FILE` is an indexed file, and the `TRANSACTION-FILE` is a line-sequential file. The program reads each record from the `TRANSACTION-FILE`, and searches for a matching record in the `MASTER-FILE`. If a match is found, the program displays the master and transaction data. If no match is found, the program displays an error message.