In this section, we will explore how to sort and merge data in COBOL. Sorting and merging are essential operations when dealing with large datasets, and COBOL provides robust features to handle these tasks efficiently.
Objectives
By the end of this section, you will be able to:
- Understand the SORT statement in COBOL.
- Use the MERGE statement to combine multiple sorted files.
- Implement practical examples of sorting and merging data.
- Solve exercises to reinforce the learned concepts.
Sorting Data
The SORT Statement
The SORT statement in COBOL is used to arrange records in a specified order. The basic syntax of the SORT statement is as follows:
file-name: The name of the file to be sorted.ASCENDING/DESCENDING KEY: Specifies the order of sorting.key-name: The field on which the sorting is based.USING input-file: The file containing the unsorted records.GIVING output-file: The file where the sorted records will be stored.
Example: Sorting Records
Let's consider an example where we have an input file containing employee records, and we want to sort these records by employee ID in ascending order.
Input File (EMPLOYEE-IN):
COBOL Program:
IDENTIFICATION DIVISION.
PROGRAM-ID. SortExample.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT EMPLOYEE-IN ASSIGN TO 'employee-in.dat'.
SELECT EMPLOYEE-OUT ASSIGN TO 'employee-out.dat'.
DATA DIVISION.
FILE SECTION.
FD EMPLOYEE-IN.
01 EMPLOYEE-RECORD-IN.
05 EMP-ID-IN PIC 9(4).
05 EMP-NAME-IN PIC X(20).
FD EMPLOYEE-OUT.
01 EMPLOYEE-RECORD-OUT.
05 EMP-ID-OUT PIC 9(4).
05 EMP-NAME-OUT PIC X(20).
WORKING-STORAGE SECTION.
01 SORT-RECORD.
05 EMP-ID PIC 9(4).
05 EMP-NAME PIC X(20).
PROCEDURE DIVISION.
OPEN INPUT EMPLOYEE-IN
OPEN OUTPUT EMPLOYEE-OUT
SORT SORT-RECORD
ON ASCENDING KEY EMP-ID
USING EMPLOYEE-IN
GIVING EMPLOYEE-OUT
CLOSE EMPLOYEE-IN
CLOSE EMPLOYEE-OUT
STOP RUN.Output File (EMPLOYEE-OUT):
Explanation
- File Declarations: We declare the input and output files in the FILE SECTION.
- SORT Statement: The
SORTstatement sorts the records inEMPLOYEE-INbased onEMP-IDin ascending order and writes the sorted records toEMPLOYEE-OUT.
Merging Data
The MERGE Statement
The MERGE statement in COBOL is used to combine multiple sorted files into a single sorted file. The basic syntax of the MERGE statement is as follows:
MERGE file-name
ON ASCENDING/DESCENDING KEY key-name
USING input-file-1 input-file-2 ...
GIVING output-file.file-name: The name of the file to be merged.ASCENDING/DESCENDING KEY: Specifies the order of merging.key-name: The field on which the merging is based.USING input-file-1 input-file-2 ...: The sorted input files to be merged.GIVING output-file: The file where the merged records will be stored.
Example: Merging Records
Let's consider an example where we have two sorted input files containing employee records, and we want to merge these records into a single sorted file.
Input File 1 (EMPLOYEE-IN1):
Input File 2 (EMPLOYEE-IN2):
COBOL Program:
IDENTIFICATION DIVISION.
PROGRAM-ID. MergeExample.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT EMPLOYEE-IN1 ASSIGN TO 'employee-in1.dat'.
SELECT EMPLOYEE-IN2 ASSIGN TO 'employee-in2.dat'.
SELECT EMPLOYEE-OUT ASSIGN TO 'employee-out.dat'.
DATA DIVISION.
FILE SECTION.
FD EMPLOYEE-IN1.
01 EMPLOYEE-RECORD-IN1.
05 EMP-ID-IN1 PIC 9(4).
05 EMP-NAME-IN1 PIC X(20).
FD EMPLOYEE-IN2.
01 EMPLOYEE-RECORD-IN2.
05 EMP-ID-IN2 PIC 9(4).
05 EMP-NAME-IN2 PIC X(20).
FD EMPLOYEE-OUT.
01 EMPLOYEE-RECORD-OUT.
05 EMP-ID-OUT PIC 9(4).
05 EMP-NAME-OUT PIC X(20).
WORKING-STORAGE SECTION.
01 MERGE-RECORD.
05 EMP-ID PIC 9(4).
05 EMP-NAME PIC X(20).
PROCEDURE DIVISION.
OPEN INPUT EMPLOYEE-IN1 EMPLOYEE-IN2
OPEN OUTPUT EMPLOYEE-OUT
MERGE MERGE-RECORD
ON ASCENDING KEY EMP-ID
USING EMPLOYEE-IN1 EMPLOYEE-IN2
GIVING EMPLOYEE-OUT
CLOSE EMPLOYEE-IN1 EMPLOYEE-IN2
CLOSE EMPLOYEE-OUT
STOP RUN.Output File (EMPLOYEE-OUT):
Explanation
- File Declarations: We declare the input and output files in the FILE SECTION.
- MERGE Statement: The
MERGEstatement merges the records fromEMPLOYEE-IN1andEMPLOYEE-IN2based onEMP-IDin ascending order and writes the merged records toEMPLOYEE-OUT.
Practical Exercises
Exercise 1: Sorting Student Records
Task: Write a COBOL program to sort student records by student ID in descending order.
Input File (STUDENT-IN):
Expected Output File (STUDENT-OUT):
Solution
IDENTIFICATION DIVISION.
PROGRAM-ID. SortStudentRecords.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT STUDENT-IN ASSIGN TO 'student-in.dat'.
SELECT STUDENT-OUT ASSIGN TO 'student-out.dat'.
DATA DIVISION.
FILE SECTION.
FD STUDENT-IN.
01 STUDENT-RECORD-IN.
05 STUDENT-ID-IN PIC 9(4).
05 STUDENT-NAME-IN PIC X(20).
FD STUDENT-OUT.
01 STUDENT-RECORD-OUT.
05 STUDENT-ID-OUT PIC 9(4).
05 STUDENT-NAME-OUT PIC X(20).
WORKING-STORAGE SECTION.
01 SORT-RECORD.
05 STUDENT-ID PIC 9(4).
05 STUDENT-NAME PIC X(20).
PROCEDURE DIVISION.
OPEN INPUT STUDENT-IN
OPEN OUTPUT STUDENT-OUT
SORT SORT-RECORD
ON DESCENDING KEY STUDENT-ID
USING STUDENT-IN
GIVING STUDENT-OUT
CLOSE STUDENT-IN
CLOSE STUDENT-OUT
STOP RUN.Exercise 2: Merging Product Records
Task: Write a COBOL program to merge two sorted product files into a single sorted file by product ID.
Input File 1 (PRODUCT-IN1):
Input File 2 (PRODUCT-IN2):
Expected Output File (PRODUCT-OUT):
Solution
IDENTIFICATION DIVISION.
PROGRAM-ID. MergeProductRecords.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT PRODUCT-IN1 ASSIGN TO 'product-in1.dat'.
SELECT PRODUCT-IN2 ASSIGN TO 'product-in2.dat'.
SELECT PRODUCT-OUT ASSIGN TO 'product-out.dat'.
DATA DIVISION.
FILE SECTION.
FD PRODUCT-IN1.
01 PRODUCT-RECORD-IN1.
05 PRODUCT-ID-IN1 PIC 9(4).
05 PRODUCT-NAME-IN1 PIC X(20).
FD PRODUCT-IN2.
01 PRODUCT-RECORD-IN2.
05 PRODUCT-ID-IN2 PIC 9(4).
05 PRODUCT-NAME-IN2 PIC X(20).
FD PRODUCT-OUT.
01 PRODUCT-RECORD-OUT.
05 PRODUCT-ID-OUT PIC 9(4).
05 PRODUCT-NAME-OUT PIC X(20).
WORKING-STORAGE SECTION.
01 MERGE-RECORD.
05 PRODUCT-ID PIC 9(4).
05 PRODUCT-NAME PIC X(20).
PROCEDURE DIVISION.
OPEN INPUT PRODUCT-IN1 PRODUCT-IN2
OPEN OUTPUT PRODUCT-OUT
MERGE MERGE-RECORD
ON ASCENDING KEY PRODUCT-ID
USING PRODUCT-IN1 PRODUCT-IN2
GIVING PRODUCT-OUT
CLOSE PRODUCT-IN1 PRODUCT-IN2
CLOSE PRODUCT-OUT
STOP RUN.Summary
In this section, we covered:
- The
SORTstatement to arrange records in a specified order. - The
MERGEstatement to combine multiple sorted files into a single sorted file. - Practical examples and exercises to reinforce the concepts of sorting and merging data in COBOL.
By mastering these techniques, you can efficiently manage and manipulate large datasets in your COBOL programs. In the next module, we will delve into subprograms and modular programming techniques to further enhance your COBOL skills.