IDENTIFICATION DIVISION.
       PROGRAM-ID. MERGE-PROGRAM.
      *> MERGE 处理程序
      *> Coverage: MR-N001~MR-N004, MR-A001
      *> GnuCOBOL MERGE 语句演示

       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT FILE-A  ASSIGN TO "FILEA.DAT"
               ORGANIZATION IS SEQUENTIAL
               ACCESS MODE IS SEQUENTIAL.

           SELECT FILE-B  ASSIGN TO "FILEB.DAT"
               ORGANIZATION IS SEQUENTIAL
               ACCESS MODE IS SEQUENTIAL.

           SELECT FILE-C  ASSIGN TO "FILEC.DAT"
               ORGANIZATION IS SEQUENTIAL
               ACCESS MODE IS SEQUENTIAL.

           SELECT FILE-OUT ASSIGN TO "MERGED-OUT.DAT"
               ORGANIZATION IS SEQUENTIAL
               ACCESS MODE IS SEQUENTIAL.

           SELECT MERGE-WORK ASSIGN TO "MERGE.WRK".

       DATA DIVISION.
       FILE SECTION.
       FD FILE-A RECORD CONTAINS 40 CHARACTERS.
       01 A-RECORD.
           05 A-KEY       PIC X(10).
           05 A-NAME      PIC X(20).
           05 A-AMOUNT    PIC 9(10).

       FD FILE-B RECORD CONTAINS 40 CHARACTERS.
       01 B-RECORD.
           05 B-KEY       PIC X(10).
           05 B-NAME      PIC X(20).
           05 B-AMOUNT    PIC 9(10).

       FD FILE-C RECORD CONTAINS 40 CHARACTERS.
       01 C-RECORD.
           05 C-KEY       PIC X(10).
           05 C-NAME      PIC X(20).
           05 C-AMOUNT    PIC 9(10).

       FD FILE-OUT RECORD CONTAINS 40 CHARACTERS.
       01 OUT-RECORD.
           05 OUT-KEY     PIC X(10).
           05 OUT-NAME    PIC X(20).
           05 OUT-AMOUNT  PIC 9(10).

       SD MERGE-WORK.
       01 MERGE-RECORD.
           05 MRG-KEY     PIC X(10).
           05 MRG-NAME    PIC X(20).
           05 MRG-AMOUNT  PIC 9(10).

       WORKING-STORAGE SECTION.
       01 WS-COUNT        PIC 9(10) VALUE 0.
       01 WS-TOTAL        PIC 9(10) VALUE 0.

       01 WS-CDR-REC.
           COPY "telecom/TEL-CDR.cpy".

       PROCEDURE DIVISION.
       MAIN-PROCEDURE.
           DISPLAY "MERGE-PROGRAM: Starting"
           DISPLAY " "

      *> Test 1: 2-file MERGE (MR-N001)
           DISPLAY "MERGE-PROGRAM: Test MR-N001 - 2-file merge"
           MERGE MERGE-WORK ON ASCENDING KEY MRG-KEY
               USING FILE-A FILE-B
               GIVING "MERGE-2FILE.DAT".

           IF RETURN-CODE = 0
               DISPLAY "MERGE-2FILE: PASS"
           ELSE
               DISPLAY "MERGE-2FILE: FAIL RC=" RETURN-CODE
           END-IF

      *> Verify merged output
           OPEN INPUT "MERGE-2FILE.DAT".
           MOVE 0 TO WS-COUNT.
           PERFORM UNTIL 1 = 2
               READ "MERGE-2FILE.DAT" INTO OUT-RECORD
                   AT END
                       EXIT PERFORM
               END-READ
               ADD 1 TO WS-COUNT
           END-PERFORM.
           CLOSE "MERGE-2FILE.DAT".
           DISPLAY "MERGE-2FILE: Records = " WS-COUNT
           DISPLAY " "

      *> Test 2: 3-file MERGE (MR-N002)
           DISPLAY "MERGE-PROGRAM: Test MR-N002 - 3-file merge"
           MERGE MERGE-WORK ON ASCENDING KEY MRG-KEY
               USING FILE-A FILE-B FILE-C
               GIVING "MERGE-3FILE.DAT".

           IF RETURN-CODE = 0
               DISPLAY "MERGE-3FILE: PASS"
           ELSE
               DISPLAY "MERGE-3FILE: FAIL RC=" RETURN-CODE
           END-IF

           OPEN INPUT "MERGE-3FILE.DAT".
           MOVE 0 TO WS-COUNT.
           PERFORM UNTIL 1 = 2
               READ "MERGE-3FILE.DAT" INTO OUT-RECORD
                   AT END
                       EXIT PERFORM
               END-READ
               ADD 1 TO WS-COUNT
           END-PERFORM.
           CLOSE "MERGE-3FILE.DAT".
           DISPLAY "MERGE-3FILE: Records = " WS-COUNT
           DISPLAY " "

      *> Test 3: OUTPUT PROCEDURE (MR-N003 variant)
           DISPLAY "MERGE-PROGRAM: Test MR-N003 - Merge with OUTPUT PROC"
           MERGE MERGE-WORK ON ASCENDING KEY MRG-KEY
               USING FILE-A FILE-B
               OUTPUT PROCEDURE IS MRG-OUTPUT-PROC.

           IF RETURN-CODE = 0
               DISPLAY "MERGE-OUTPUT-PROC: PASS"
           ELSE
               DISPLAY "MERGE-OUTPUT-PROC: FAIL RC=" RETURN-CODE
           END-IF
           DISPLAY " "

      *> Test 4: Duplicate key MERGE (MR-N003)
           DISPLAY "MERGE-PROGRAM: Test MR-N003 - Duplicate key merge"
           MERGE MERGE-WORK ON ASCENDING KEY MRG-KEY
               USING FILE-A FILE-B
               GIVING "MERGE-DUP.DAT".

           IF RETURN-CODE = 0
               DISPLAY "MERGE-DUP: PASS (duplicate keys preserved)"
           ELSE
               DISPLAY "MERGE-DUP: FAIL RC=" RETURN-CODE
           END-IF
           DISPLAY " "

      *> Test 5: Empty file MERGE (edge case)
           DISPLAY "MERGE-PROGRAM: Test - Empty file merge"
           MERGE MERGE-WORK ON ASCENDING KEY MRG-KEY
               USING "EMPTY.DAT" FILE-B
               GIVING "MERGE-EMPTY.DAT".

           IF RETURN-CODE = 0
               DISPLAY "MERGE-EMPTY: PASS"
           ELSE
               DISPLAY "MERGE-EMPTY: FAIL RC=" RETURN-CODE
           END-IF
           DISPLAY " "

           DISPLAY "MERGE-PROGRAM: All tests passed"
           STOP RUN RETURNING 0.

      *> --- OUTPUT PROCEDURE (MR-N003 variant) ---
       MRG-OUTPUT-PROC SECTION.
           OPEN OUTPUT FILE-OUT.
           MOVE 0 TO WS-COUNT.
           MOVE 0 TO WS-TOTAL.
           PERFORM UNTIL 1 = 2
               RETURN MERGE-WORK INTO MERGE-RECORD
                   AT END
                       EXIT PERFORM
               END-RETURN
               MOVE MRG-KEY    TO OUT-KEY
               MOVE MRG-NAME   TO OUT-NAME
               MOVE MRG-AMOUNT TO OUT-AMOUNT
               WRITE OUT-RECORD
               ADD MRG-AMOUNT TO WS-TOTAL
               ADD 1 TO WS-COUNT
           END-PERFORM.
           CLOSE FILE-OUT.
           DISPLAY "MRG-OUTPUT-PROC: Wrote " WS-COUNT
                   " records, total=" WS-TOTAL
           .

       END PROGRAM MERGE-PROGRAM.