MERGE Statement
The MERGE statement is used to combine two or more sequentially ordered files into a single, merged, and sequentially ordered output file. The files should be in sorted order according to the ascending or descending key that is common for both files.
This operation is usually required when we have multiple files with data in a similar format and want to generate a consolidated, sorted dataset. A MERGE statement can be coded anywhere in the procedure division except in a declarative section.
Syntax -
MERGE work-file-1
ON ASCENDING/DESCENDING KEY key-name-1 [key-name-2 ...]
[COLLATING SEQUENCE {IS} alphabet-name-1]
[USING input-file-1 [, input-file-2, ...]]
[OUTPUT PROCEDURE IS para-1 THRU para-2]
[GIVING output-file-1 [, output-file-2, ...]]Parameters -
- work-file-1 - The name of the merge work file. It's a logical file and does not correspond to any physical file.
- ON ASCENDING/DESCENDING KEY - Defines the sorting order for the merge based on the specified keys.
- key-name-1, key-name-2, ... - Specifies the data items that determine the sort order.
- COLLATING SEQUENCE {IS} alphabet-name-1 - Optional. Specifies the collating sequence for sorting. If not mentioned, machine's native sequence is used.
- USING input-file-1, input-file-2, ... - Specifies the input files that we want to merge. They should be sorted in the sequence mentioned by the sort keys.
- OUTPUT PROCEDURE IS para-1 THRU para-2 - Specifies the name of a procedure used to select or modify output records from the merge operation.
- GIVING output-file-1, output-file-2, ... - Specifies the output file or files to which the merged records are written.
Merge processing steps -
- It opens work file in I-O mode, input files in INPUT mode, and output file in OUTPUT mode.
- Transfers the records from all input files to the work file using the order coded with key-name-1.
- Transfers the sorted records from work file to output file.
- Closes the input, output files and releases (deletes) the work-file.
Practical Example -
Scenario - Let us assume two different employee files contain employee information, and create one merged file containing all employee details from two files.
Input -
MATEPK.EMPFILE.INPUT1
----+----1----+----2----+----3----+----4----+-- E0001EMPLOYEE1 DIR LOC1 0000100000 E0002EMPLOYEE2 MGR DEPT1LOC1 0000080000 E0004EMPLOYEE4 TL DEPT1LOC1 0000050000 E0006EMPLOYEE6 SE DEPT1LOC1 0000034000
MATEPK.EMPFILE.INPUT2
----+----1----+----2----+----3----+----4----+-- E0003EMPLOYEE3 MGR DEPT2LOC2 0000075000 E0005EMPLOYEE5 SSE DEPT1LOC1 0000045000 E0007EMPLOYEE7 SSE DEPT2LOC2 0000046000
Code -
----+----1----+----2----+----3----+----4----+----5----+
IDENTIFICATION DIVISION.
PROGRAM-ID. MERGEFLS.
AUTHOR. MTH.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT EMPFILE1 ASSIGN TO INPUT1.
SELECT EMPFILE2 ASSIGN TO INPUT2.
SELECT EMPFILEO ASSIGN TO OUTPUT1.
SELECT WORKFILE ASSIGN TO WORK1.
DATA DIVISION.
FILE SECTION.
* Input File1
FD EMPFILE1
RECORD CONTAINS 47 CHARACTERS
DATA RECORD EMP-REC1
RECORDING MODE F.
01 EMP-REC1.
COPY EMPREC.
* Input File2
FD EMPFILE2
RECORD CONTAINS 47 CHARACTERS
DATA RECORD EMP-REC2
RECORDING MODE F.
01 EMP-REC2.
COPY EMPREC.
* Output file
FD EMPFILEO
RECORD CONTAINS 47 CHARACTERS
DATA RECORD EMP-RECO
RECORDING MODE F.
01 EMP-RECO.
COPY EMPREC.
* Merge work file
SD WORKFILE
RECORD CONTAINS 47 CHARACTERS
DATA RECORD WORK-REC
RECORDING MODE F.
01 WORK-REC.
05 WORK-EMP-NUM PIC 9(05).
05 WORK-REM-REC PIC X(42).
PROCEDURE DIVISION.
MERGE WORKFILE
ON ASCENDING KEY WORK-EMP-NUM
USING EMPFILE1, EMPFILE2
GIVING EMPFILEO.
STOP RUN.JCL -
//MATEPKRJ JOB MSGLEVEL=(1,1),NOTIFY=&SYSUID //* //STEP01 EXEC PGM=MERGEFLS //STEPLIB DD DSN=MATEPK.COBOL.LOADLIB,DISP=SHR //INPUT1 DD DSN=MATEPK.EMPFILE.INPUT1,DISP=SHR //INPUT2 DD DSN=MATEPK.EMPFILE.INPUT2,DISP=SHR //OUTPUT1 DD DSN=MATEPK.EMPFILE.OUTPUT1, // DISP=(NEW,CATLG,DELETE), // SPACE=(TRK,(3,2),RLSE), // UNIT=SYSDA, // DCB=(DSORG=PS,RECFM=FB,LRECL=47,BLKSIZE=470) //WORK1 DD DSN=&&TEMP, // DISP=(NEW,DELETE,DELETE), // SPACE=(CYL,(10,5),RLSE), // UNIT=SYSDA, // DCB=(DSORG=PS,RECFM=FB,LRECL=47,BLKSIZE=470) //SYSOUT DD SYSOUT=*
Output (MATEPK.EMPFILE.OUTPUT1) -
----+----1----+----2----+----3----+----4----+-- E0001EMPLOYEE1 DIR LOC1 0000100000 E0002EMPLOYEE2 MGR DEPT1LOC1 0000080000 E0003EMPLOYEE3 MGR DEPT2LOC2 0000075000 E0004EMPLOYEE4 TL DEPT1LOC1 0000050000 E0005EMPLOYEE5 SSE DEPT1LOC1 0000045000 E0006EMPLOYEE6 SE DEPT1LOC1 0000034000 E0007EMPLOYEE7 SSE DEPT2LOC2 0000046000
Explaining Example -
In the above example, MERGE statement merges two sorted input files based on the employee number (1-5 bytes) in both files and writes into the output files.