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COBOL Tutorial

COBOL ALTERNATE Clause

The ALTERNATE clause represents one of COBOL's most sophisticated and powerful file organization mechanisms, serving as the primary tool for defining alternate keys in indexed files that enable multiple access paths to the same data records. Far more than a simple file access method, the ALTERNATE clause embodies COBOL's comprehensive approach to data organization by providing secondary indexing capabilities, multiple sort sequences, flexible data retrieval patterns, and advanced file navigation techniques that enable applications to access the same data through different logical views while maintaining data integrity, performance optimization, and sophisticated query capabilities that are essential for complex business applications requiring multiple data access patterns and comprehensive information retrieval systems.

In enterprise computing environments, the ALTERNATE clause serves as a critical foundation for advanced database-like functionality within COBOL file systems, enabling developers to create sophisticated data access applications that support multiple search criteria, implement complex reporting requirements, provide flexible data navigation, and maintain high-performance data retrieval capabilities. Its capabilities extend far beyond simple sequential access to encompass sophisticated indexing strategies, duplicate key handling, partial key searches, and integration with modern database concepts that are essential for applications requiring comprehensive data access flexibility and enterprise-grade file management capabilities that support complex business data organization requirements and advanced information retrieval patterns.

ALTERNATE Clause Fundamentals

Basic ALTERNATE Key Definition

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*> Basic ALTERNATE key definition in SELECT statement
SELECT CUSTOMER-FILE ASSIGN TO "CUSTOMER.DAT"
    ORGANIZATION IS INDEXED
    ACCESS MODE IS DYNAMIC
    RECORD KEY IS CUSTOMER-ID
    ALTERNATE RECORD KEY IS CUSTOMER-NAME
    ALTERNATE RECORD KEY IS CUSTOMER-ZIP-CODE
    ALTERNATE RECORD KEY IS CUSTOMER-PHONE
    FILE STATUS IS CUSTOMER-FILE-STATUS.
 
*> File record structure
FD  CUSTOMER-FILE.
01  CUSTOMER-RECORD.
    05  CUSTOMER-ID           PIC X(10).
    05  CUSTOMER-NAME         PIC X(30).
    05  CUSTOMER-ADDRESS      PIC X(50).
    05  CUSTOMER-CITY         PIC X(20).
    05  CUSTOMER-STATE        PIC X(2).
    05  CUSTOMER-ZIP-CODE     PIC X(10).
    05  CUSTOMER-PHONE        PIC X(15).
    05  CUSTOMER-EMAIL        PIC X(40).
    05  CUSTOMER-STATUS       PIC X(10).
 
*> Working storage for key fields
01  WS-SEARCH-KEYS.
    05  WS-SEARCH-NAME        PIC X(30).
    05  WS-SEARCH-ZIP         PIC X(10).
    05  WS-SEARCH-PHONE       PIC X(15).

Basic ALTERNATE key definitions create secondary access paths to indexed file data.

ALTERNATE Keys with Duplicates

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*> ALTERNATE keys allowing duplicate values
SELECT EMPLOYEE-FILE ASSIGN TO "EMPLOYEE.DAT"
    ORGANIZATION IS INDEXED
    ACCESS MODE IS DYNAMIC
    RECORD KEY IS EMPLOYEE-ID
    ALTERNATE RECORD KEY IS DEPARTMENT-CODE WITH DUPLICATES
    ALTERNATE RECORD KEY IS SALARY-GRADE WITH DUPLICATES
    ALTERNATE RECORD KEY IS HIRE-DATE WITH DUPLICATES
    ALTERNATE RECORD KEY IS LAST-NAME WITH DUPLICATES
    FILE STATUS IS EMPLOYEE-FILE-STATUS.
 
*> Employee record structure
FD  EMPLOYEE-FILE.
01  EMPLOYEE-RECORD.
    05  EMPLOYEE-ID           PIC X(8).
    05  FIRST-NAME            PIC X(20).
    05  LAST-NAME             PIC X(25).
    05  DEPARTMENT-CODE       PIC X(5).
    05  SALARY-GRADE          PIC X(3).
    05  HIRE-DATE             PIC X(8).
    05  SALARY-AMOUNT         PIC 9(7)V99.
    05  MANAGER-ID            PIC X(8).
    05  EMPLOYEE-STATUS       PIC X(10).
 
*> Search criteria for duplicate keys
01  WS-DEPARTMENT-SEARCH.
    05  WS-DEPT-CODE          PIC X(5).
    05  WS-DEPT-COUNTER       PIC 9(5) VALUE 0.
 
01  WS-SALARY-SEARCH.
    05  WS-SALARY-GRADE       PIC X(3).
    05  WS-SALARY-COUNTER     PIC 9(5) VALUE 0.

WITH DUPLICATES clause allows multiple records with the same alternate key value.

Complex ALTERNATE Key Structures

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*> Complex ALTERNATE keys with compound fields
SELECT INVENTORY-FILE ASSIGN TO "INVENTORY.DAT"
    ORGANIZATION IS INDEXED
    ACCESS MODE IS DYNAMIC
    RECORD KEY IS ITEM-ID
    ALTERNATE RECORD KEY IS CATEGORY-SUBCATEGORY-KEY
        = ITEM-CATEGORY, ITEM-SUBCATEGORY
    ALTERNATE RECORD KEY IS SUPPLIER-ITEM-KEY
        = SUPPLIER-CODE, ITEM-NUMBER WITH DUPLICATES
    ALTERNATE RECORD KEY IS LOCATION-STATUS-KEY
        = WAREHOUSE-LOCATION, ITEM-STATUS
    ALTERNATE RECORD KEY IS PRICE-RANGE-KEY
        = PRICE-CATEGORY, ITEM-PRIORITY WITH DUPLICATES
    FILE STATUS IS INVENTORY-FILE-STATUS.
 
*> Inventory record with compound key fields
FD  INVENTORY-FILE.
01  INVENTORY-RECORD.
    05  ITEM-ID               PIC X(12).
    05  ITEM-NUMBER           PIC X(15).
    05  ITEM-DESCRIPTION      PIC X(50).
    05  ITEM-CATEGORY         PIC X(10).
    05  ITEM-SUBCATEGORY      PIC X(10).
    05  SUPPLIER-CODE         PIC X(8).
    05  WAREHOUSE-LOCATION    PIC X(6).
    05  ITEM-STATUS           PIC X(10).
    05  PRICE-CATEGORY        PIC X(5).
    05  ITEM-PRIORITY         PIC X(3).
    05  UNIT-PRICE            PIC 9(6)V99.
    05  QUANTITY-ON-HAND      PIC 9(8).
    05  REORDER-LEVEL         PIC 9(6).
 
*> Compound key search structures
01  WS-COMPOUND-KEYS.
    05  WS-CATEGORY-SUBCATEGORY-KEY.
        10  WS-SEARCH-CATEGORY    PIC X(10).
        10  WS-SEARCH-SUBCATEGORY PIC X(10).
    
    05  WS-SUPPLIER-ITEM-KEY.
        10  WS-SEARCH-SUPPLIER    PIC X(8).
        10  WS-SEARCH-ITEM-NUM    PIC X(15).
    
    05  WS-LOCATION-STATUS-KEY.
        10  WS-SEARCH-LOCATION    PIC X(6).
        10  WS-SEARCH-STATUS      PIC X(10).

Compound ALTERNATE keys combine multiple fields for sophisticated data organization.

Comprehensive Example

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IDENTIFICATION DIVISION.
PROGRAM-ID. ALTERNATE-KEY-DEMO.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    *> Customer master file with multiple alternate keys
    SELECT CUSTOMER-MASTER-FILE ASSIGN TO "CUSTMAST.DAT"
        ORGANIZATION IS INDEXED
        ACCESS MODE IS DYNAMIC
        RECORD KEY IS CUSTOMER-ID
        ALTERNATE RECORD KEY IS CUSTOMER-NAME WITH DUPLICATES
        ALTERNATE RECORD KEY IS CUSTOMER-ZIP-CODE WITH DUPLICATES
        ALTERNATE RECORD KEY IS CUSTOMER-PHONE
        ALTERNATE RECORD KEY IS CUSTOMER-EMAIL
        ALTERNATE RECORD KEY IS ACCOUNT-STATUS-KEY
            = ACCOUNT-STATUS, CREDIT-RATING WITH DUPLICATES
        FILE STATUS IS CUSTOMER-FILE-STATUS.
    
    *> Transaction file with alternate keys
    SELECT TRANSACTION-FILE ASSIGN TO "TRANS.DAT"
        ORGANIZATION IS INDEXED
        ACCESS MODE IS DYNAMIC
        RECORD KEY IS TRANSACTION-ID
        ALTERNATE RECORD KEY IS CUSTOMER-TRANS-KEY
            = CUSTOMER-ID, TRANSACTION-DATE WITH DUPLICATES
        ALTERNATE RECORD KEY IS DATE-TYPE-KEY
            = TRANSACTION-DATE, TRANSACTION-TYPE WITH DUPLICATES
        ALTERNATE RECORD KEY IS AMOUNT-RANGE-KEY
            = AMOUNT-CATEGORY, TRANSACTION-STATUS WITH DUPLICATES
        FILE STATUS IS TRANSACTION-FILE-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  CUSTOMER-MASTER-FILE.
01  CUSTOMER-MASTER-RECORD.
    05  CUSTOMER-ID           PIC X(10).
    05  CUSTOMER-NAME         PIC X(30).
    05  CUSTOMER-ADDRESS      PIC X(50).
    05  CUSTOMER-CITY         PIC X(20).
    05  CUSTOMER-STATE        PIC X(2).
    05  CUSTOMER-ZIP-CODE     PIC X(10).
    05  CUSTOMER-PHONE        PIC X(15).
    05  CUSTOMER-EMAIL        PIC X(40).
    05  ACCOUNT-STATUS        PIC X(10).
    05  CREDIT-RATING         PIC X(5).
    05  ACCOUNT-BALANCE       PIC S9(8)V99.
    05  LAST-ACTIVITY-DATE    PIC X(8).
 
FD  TRANSACTION-FILE.
01  TRANSACTION-RECORD.
    05  TRANSACTION-ID        PIC X(15).
    05  CUSTOMER-ID           PIC X(10).
    05  TRANSACTION-DATE      PIC X(8).
    05  TRANSACTION-TYPE      PIC X(10).
    05  TRANSACTION-AMOUNT    PIC S9(8)V99.
    05  AMOUNT-CATEGORY       PIC X(5).
    05  TRANSACTION-STATUS    PIC X(10).
    05  DESCRIPTION           PIC X(50).
    05  REFERENCE-NUMBER      PIC X(20).
 
WORKING-STORAGE SECTION.
*> File status variables
01  CUSTOMER-FILE-STATUS      PIC X(2).
    88  CUSTOMER-FILE-OK      VALUE "00".
    88  CUSTOMER-EOF          VALUE "10".
    88  CUSTOMER-NOT-FOUND    VALUE "23".
 
01  TRANSACTION-FILE-STATUS   PIC X(2).
    88  TRANSACTION-FILE-OK   VALUE "00".
    88  TRANSACTION-EOF       VALUE "10".
    88  TRANSACTION-NOT-FOUND VALUE "23".
 
*> Search key structures
01  WS-SEARCH-CRITERIA.
    05  WS-SEARCH-NAME        PIC X(30).
    05  WS-SEARCH-ZIP         PIC X(10).
    05  WS-SEARCH-PHONE       PIC X(15).
    05  WS-SEARCH-EMAIL       PIC X(40).
    05  WS-SEARCH-STATUS      PIC X(10).
    05  WS-SEARCH-RATING      PIC X(5).
 
*> Compound key search structures
01  WS-COMPOUND-SEARCH-KEYS.
    05  WS-ACCOUNT-STATUS-KEY.
        10  WS-STATUS-SEARCH  PIC X(10).
        10  WS-RATING-SEARCH  PIC X(5).
    
    05  WS-CUSTOMER-TRANS-KEY.
        10  WS-CUST-ID-SEARCH PIC X(10).
        10  WS-TRANS-DATE-SEARCH PIC X(8).
    
    05  WS-DATE-TYPE-KEY.
        10  WS-DATE-SEARCH    PIC X(8).
        10  WS-TYPE-SEARCH    PIC X(10).
    
    05  WS-AMOUNT-RANGE-KEY.
        10  WS-AMOUNT-CAT-SEARCH PIC X(5).
        10  WS-TRANS-STATUS-SEARCH PIC X(10).
 
*> Processing counters and flags
01  WS-PROCESSING-COUNTERS.
    05  WS-RECORDS-READ       PIC 9(7) VALUE 0.
    05  WS-RECORDS-FOUND      PIC 9(7) VALUE 0.
    05  WS-DUPLICATE-COUNT    PIC 9(5) VALUE 0.
    05  WS-SEARCH-COUNT       PIC 9(5) VALUE 0.
 
*> Display and formatting variables
01  WS-DISPLAY-FIELDS.
    05  WS-FORMATTED-AMOUNT   PIC $$$,$$$,$$9.99.
    05  WS-FORMATTED-DATE     PIC X(2)/X(2)/X(4).
    05  WS-FORMATTED-PHONE    PIC X(3)-X(3)-X(4).
 
*> Menu and control variables
01  WS-MENU-CONTROL.
    05  WS-MENU-CHOICE        PIC X(1).
    05  WS-CONTINUE-FLAG      PIC X(1) VALUE "Y".
        88  CONTINUE-PROCESSING VALUE "Y".
        88  STOP-PROCESSING   VALUE "N".
 
PROCEDURE DIVISION.
MAIN-PROCESSING.
    DISPLAY "=== ALTERNATE Key Demonstration ===".
    DISPLAY " ".
    
    PERFORM OPEN-FILES
    PERFORM DEMONSTRATE-ALTERNATE-KEY-USAGE
    PERFORM CLOSE-FILES
    
    DISPLAY " ".
    DISPLAY "ALTERNATE key demonstration completed successfully".
    STOP RUN.
 
OPEN-FILES.
    OPEN I-O CUSTOMER-MASTER-FILE.
    IF NOT CUSTOMER-FILE-OK
        DISPLAY "Error opening customer file: " CUSTOMER-FILE-STATUS
        STOP RUN
    END-IF.
    
    OPEN I-O TRANSACTION-FILE.
    IF NOT TRANSACTION-FILE-OK
        DISPLAY "Error opening transaction file: " TRANSACTION-FILE-STATUS
        STOP RUN
    END-IF.
 
DEMONSTRATE-ALTERNATE-KEY-USAGE.
    PERFORM UNTIL STOP-PROCESSING
        PERFORM DISPLAY-MENU
        PERFORM GET-MENU-CHOICE
        PERFORM PROCESS-MENU-CHOICE
    END-PERFORM.
 
DISPLAY-MENU.
    DISPLAY " ".
    DISPLAY "ALTERNATE Key Search Options:".
    DISPLAY "=============================".
    DISPLAY "1. Search by Customer Name".
    DISPLAY "2. Search by ZIP Code".
    DISPLAY "3. Search by Phone Number".
    DISPLAY "4. Search by Email Address".
    DISPLAY "5. Search by Account Status and Credit Rating".
    DISPLAY "6. Search Transactions by Customer and Date".
    DISPLAY "7. Search Transactions by Date and Type".
    DISPLAY "8. Search Transactions by Amount Category".
    DISPLAY "9. Demonstrate Duplicate Key Processing".
    DISPLAY "0. Exit".
    DISPLAY " ".
 
GET-MENU-CHOICE.
    DISPLAY "Enter your choice (0-9): " WITH NO ADVANCING.
    ACCEPT WS-MENU-CHOICE.
 
PROCESS-MENU-CHOICE.
    EVALUATE WS-MENU-CHOICE
        WHEN "1"
            PERFORM SEARCH-BY-CUSTOMER-NAME
        WHEN "2"
            PERFORM SEARCH-BY-ZIP-CODE
        WHEN "3"
            PERFORM SEARCH-BY-PHONE
        WHEN "4"
            PERFORM SEARCH-BY-EMAIL
        WHEN "5"
            PERFORM SEARCH-BY-STATUS-RATING
        WHEN "6"
            PERFORM SEARCH-TRANSACTIONS-BY-CUSTOMER-DATE
        WHEN "7"
            PERFORM SEARCH-TRANSACTIONS-BY-DATE-TYPE
        WHEN "8"
            PERFORM SEARCH-TRANSACTIONS-BY-AMOUNT-CATEGORY
        WHEN "9"
            PERFORM DEMONSTRATE-DUPLICATE-PROCESSING
        WHEN "0"
            SET STOP-PROCESSING TO TRUE
        WHEN OTHER
            DISPLAY "Invalid choice. Please try again."
    END-EVALUATE.
 
SEARCH-BY-CUSTOMER-NAME.
    DISPLAY " ".
    DISPLAY "Search by Customer Name:".
    DISPLAY "========================".
    DISPLAY "Enter customer name: " WITH NO ADVANCING.
    ACCEPT WS-SEARCH-NAME.
    
    MOVE WS-SEARCH-NAME TO CUSTOMER-NAME.
    START CUSTOMER-MASTER-FILE
        KEY IS EQUAL TO CUSTOMER-NAME
        INVALID KEY
            DISPLAY "No customer found with name: " WS-SEARCH-NAME
        NOT INVALID KEY
            PERFORM READ-AND-DISPLAY-CUSTOMER
    END-START.
 
SEARCH-BY-ZIP-CODE.
    DISPLAY " ".
    DISPLAY "Search by ZIP Code:".
    DISPLAY "===================".
    DISPLAY "Enter ZIP code: " WITH NO ADVANCING.
    ACCEPT WS-SEARCH-ZIP.
    
    MOVE WS-SEARCH-ZIP TO CUSTOMER-ZIP-CODE.
    START CUSTOMER-MASTER-FILE
        KEY IS EQUAL TO CUSTOMER-ZIP-CODE
        INVALID KEY
            DISPLAY "No customers found in ZIP code: " WS-SEARCH-ZIP
        NOT INVALID KEY
            PERFORM READ-ALL-CUSTOMERS-IN-ZIP
    END-START.
 
SEARCH-BY-PHONE.
    DISPLAY " ".
    DISPLAY "Search by Phone Number:".
    DISPLAY "=======================".
    DISPLAY "Enter phone number: " WITH NO ADVANCING.
    ACCEPT WS-SEARCH-PHONE.
    
    MOVE WS-SEARCH-PHONE TO CUSTOMER-PHONE.
    START CUSTOMER-MASTER-FILE
        KEY IS EQUAL TO CUSTOMER-PHONE
        INVALID KEY
            DISPLAY "No customer found with phone: " WS-SEARCH-PHONE
        NOT INVALID KEY
            PERFORM READ-AND-DISPLAY-CUSTOMER
    END-START.
 
SEARCH-BY-EMAIL.
    DISPLAY " ".
    DISPLAY "Search by Email Address:".
    DISPLAY "========================".
    DISPLAY "Enter email address: " WITH NO ADVANCING.
    ACCEPT WS-SEARCH-EMAIL.
    
    MOVE WS-SEARCH-EMAIL TO CUSTOMER-EMAIL.
    START CUSTOMER-MASTER-FILE
        KEY IS EQUAL TO CUSTOMER-EMAIL
        INVALID KEY
            DISPLAY "No customer found with email: " WS-SEARCH-EMAIL
        NOT INVALID KEY
            PERFORM READ-AND-DISPLAY-CUSTOMER
    END-START.
 
SEARCH-BY-STATUS-RATING.
    DISPLAY " ".
    DISPLAY "Search by Account Status and Credit Rating:".
    DISPLAY "===========================================".
    DISPLAY "Enter account status: " WITH NO ADVANCING.
    ACCEPT WS-STATUS-SEARCH.
    DISPLAY "Enter credit rating: " WITH NO ADVANCING.
    ACCEPT WS-RATING-SEARCH.
    
    MOVE WS-STATUS-SEARCH TO ACCOUNT-STATUS.
    MOVE WS-RATING-SEARCH TO CREDIT-RATING.
    START CUSTOMER-MASTER-FILE
        KEY IS EQUAL TO ACCOUNT-STATUS-KEY
        INVALID KEY
            DISPLAY "No customers found with status: " WS-STATUS-SEARCH
                    " and rating: " WS-RATING-SEARCH
        NOT INVALID KEY
            PERFORM READ-ALL-CUSTOMERS-BY-STATUS-RATING
    END-START.
 
SEARCH-TRANSACTIONS-BY-CUSTOMER-DATE.
    DISPLAY " ".
    DISPLAY "Search Transactions by Customer and Date:".
    DISPLAY "=========================================".
    DISPLAY "Enter customer ID: " WITH NO ADVANCING.
    ACCEPT WS-CUST-ID-SEARCH.
    DISPLAY "Enter transaction date (YYYYMMDD): " WITH NO ADVANCING.
    ACCEPT WS-TRANS-DATE-SEARCH.
    
    MOVE WS-CUST-ID-SEARCH TO CUSTOMER-ID OF TRANSACTION-RECORD.
    MOVE WS-TRANS-DATE-SEARCH TO TRANSACTION-DATE.
    START TRANSACTION-FILE
        KEY IS EQUAL TO CUSTOMER-TRANS-KEY
        INVALID KEY
            DISPLAY "No transactions found for customer: " WS-CUST-ID-SEARCH
                    " on date: " WS-TRANS-DATE-SEARCH
        NOT INVALID KEY
            PERFORM READ-ALL-CUSTOMER-TRANSACTIONS
    END-START.
 
SEARCH-TRANSACTIONS-BY-DATE-TYPE.
    DISPLAY " ".
    DISPLAY "Search Transactions by Date and Type:".
    DISPLAY "=====================================".
    DISPLAY "Enter transaction date (YYYYMMDD): " WITH NO ADVANCING.
    ACCEPT WS-DATE-SEARCH.
    DISPLAY "Enter transaction type: " WITH NO ADVANCING.
    ACCEPT WS-TYPE-SEARCH.
    
    MOVE WS-DATE-SEARCH TO TRANSACTION-DATE.
    MOVE WS-TYPE-SEARCH TO TRANSACTION-TYPE.
    START TRANSACTION-FILE
        KEY IS EQUAL TO DATE-TYPE-KEY
        INVALID KEY
            DISPLAY "No transactions found for date: " WS-DATE-SEARCH
                    " and type: " WS-TYPE-SEARCH
        NOT INVALID KEY
            PERFORM READ-ALL-DATE-TYPE-TRANSACTIONS
    END-START.
 
SEARCH-TRANSACTIONS-BY-AMOUNT-CATEGORY.
    DISPLAY " ".
    DISPLAY "Search Transactions by Amount Category:".
    DISPLAY "=======================================".
    DISPLAY "Enter amount category: " WITH NO ADVANCING.
    ACCEPT WS-AMOUNT-CAT-SEARCH.
    DISPLAY "Enter transaction status: " WITH NO ADVANCING.
    ACCEPT WS-TRANS-STATUS-SEARCH.
    
    MOVE WS-AMOUNT-CAT-SEARCH TO AMOUNT-CATEGORY.
    MOVE WS-TRANS-STATUS-SEARCH TO TRANSACTION-STATUS.
    START TRANSACTION-FILE
        KEY IS EQUAL TO AMOUNT-RANGE-KEY
        INVALID KEY
            DISPLAY "No transactions found for category: " WS-AMOUNT-CAT-SEARCH
                    " and status: " WS-TRANS-STATUS-SEARCH
        NOT INVALID KEY
            PERFORM READ-ALL-AMOUNT-CATEGORY-TRANSACTIONS
    END-START.
 
READ-AND-DISPLAY-CUSTOMER.
    READ CUSTOMER-MASTER-FILE NEXT RECORD.
    IF CUSTOMER-FILE-OK
        PERFORM DISPLAY-CUSTOMER-DETAILS
        ADD 1 TO WS-RECORDS-FOUND
    ELSE
        DISPLAY "Error reading customer record: " CUSTOMER-FILE-STATUS
    END-IF.
 
READ-ALL-CUSTOMERS-IN-ZIP.
    MOVE 0 TO WS-DUPLICATE-COUNT.
    PERFORM UNTIL NOT CUSTOMER-FILE-OK OR CUSTOMER-EOF
        READ CUSTOMER-MASTER-FILE NEXT RECORD
        IF CUSTOMER-FILE-OK
            IF CUSTOMER-ZIP-CODE = WS-SEARCH-ZIP
                ADD 1 TO WS-DUPLICATE-COUNT
                PERFORM DISPLAY-CUSTOMER-SUMMARY
            ELSE
                SET CUSTOMER-EOF TO TRUE
            END-IF
        END-IF
    END-PERFORM.
    
    DISPLAY "Total customers found in ZIP " WS-SEARCH-ZIP ": " 
            WS-DUPLICATE-COUNT.
 
READ-ALL-CUSTOMERS-BY-STATUS-RATING.
    MOVE 0 TO WS-DUPLICATE-COUNT.
    PERFORM UNTIL NOT CUSTOMER-FILE-OK OR CUSTOMER-EOF
        READ CUSTOMER-MASTER-FILE NEXT RECORD
        IF CUSTOMER-FILE-OK
            IF ACCOUNT-STATUS = WS-STATUS-SEARCH AND
               CREDIT-RATING = WS-RATING-SEARCH
                ADD 1 TO WS-DUPLICATE-COUNT
                PERFORM DISPLAY-CUSTOMER-SUMMARY
            ELSE
                SET CUSTOMER-EOF TO TRUE
            END-IF
        END-IF
    END-PERFORM.
    
    DISPLAY "Total customers found with status " WS-STATUS-SEARCH
            " and rating " WS-RATING-SEARCH ": " WS-DUPLICATE-COUNT.
 
READ-ALL-CUSTOMER-TRANSACTIONS.
    MOVE 0 TO WS-DUPLICATE-COUNT.
    PERFORM UNTIL NOT TRANSACTION-FILE-OK OR TRANSACTION-EOF
        READ TRANSACTION-FILE NEXT RECORD
        IF TRANSACTION-FILE-OK
            IF CUSTOMER-ID OF TRANSACTION-RECORD = WS-CUST-ID-SEARCH AND
               TRANSACTION-DATE = WS-TRANS-DATE-SEARCH
                ADD 1 TO WS-DUPLICATE-COUNT
                PERFORM DISPLAY-TRANSACTION-SUMMARY
            ELSE
                SET TRANSACTION-EOF TO TRUE
            END-IF
        END-IF
    END-PERFORM.
    
    DISPLAY "Total transactions found: " WS-DUPLICATE-COUNT.
 
READ-ALL-DATE-TYPE-TRANSACTIONS.
    MOVE 0 TO WS-DUPLICATE-COUNT.
    PERFORM UNTIL NOT TRANSACTION-FILE-OK OR TRANSACTION-EOF
        READ TRANSACTION-FILE NEXT RECORD
        IF TRANSACTION-FILE-OK
            IF TRANSACTION-DATE = WS-DATE-SEARCH AND
               TRANSACTION-TYPE = WS-TYPE-SEARCH
                ADD 1 TO WS-DUPLICATE-COUNT
                PERFORM DISPLAY-TRANSACTION-SUMMARY
            ELSE
                SET TRANSACTION-EOF TO TRUE
            END-IF
        END-IF
    END-PERFORM.
    
    DISPLAY "Total transactions found: " WS-DUPLICATE-COUNT.
 
READ-ALL-AMOUNT-CATEGORY-TRANSACTIONS.
    MOVE 0 TO WS-DUPLICATE-COUNT.
    PERFORM UNTIL NOT TRANSACTION-FILE-OK OR TRANSACTION-EOF
        READ TRANSACTION-FILE NEXT RECORD
        IF TRANSACTION-FILE-OK
            IF AMOUNT-CATEGORY = WS-AMOUNT-CAT-SEARCH AND
               TRANSACTION-STATUS = WS-TRANS-STATUS-SEARCH
                ADD 1 TO WS-DUPLICATE-COUNT
                PERFORM DISPLAY-TRANSACTION-SUMMARY
            ELSE
                SET TRANSACTION-EOF TO TRUE
            END-IF
        END-IF
    END-PERFORM.
    
    DISPLAY "Total transactions found: " WS-DUPLICATE-COUNT.
 
DISPLAY-CUSTOMER-DETAILS.
    DISPLAY " ".
    DISPLAY "Customer Details:".
    DISPLAY "================".
    DISPLAY "Customer ID: " CUSTOMER-ID.
    DISPLAY "Name: " CUSTOMER-NAME.
    DISPLAY "Address: " CUSTOMER-ADDRESS.
    DISPLAY "City: " CUSTOMER-CITY ", " CUSTOMER-STATE " " CUSTOMER-ZIP-CODE.
    
    MOVE CUSTOMER-PHONE TO WS-FORMATTED-PHONE.
    DISPLAY "Phone: " WS-FORMATTED-PHONE.
    DISPLAY "Email: " CUSTOMER-EMAIL.
    DISPLAY "Account Status: " ACCOUNT-STATUS.
    DISPLAY "Credit Rating: " CREDIT-RATING.
    
    MOVE ACCOUNT-BALANCE TO WS-FORMATTED-AMOUNT.
    DISPLAY "Account Balance: " WS-FORMATTED-AMOUNT.
    
    MOVE LAST-ACTIVITY-DATE TO WS-FORMATTED-DATE.
    DISPLAY "Last Activity: " WS-FORMATTED-DATE.
 
DISPLAY-CUSTOMER-SUMMARY.
    DISPLAY CUSTOMER-ID " - " CUSTOMER-NAME " - " CUSTOMER-ZIP-CODE.
 
DISPLAY-TRANSACTION-SUMMARY.
    MOVE TRANSACTION-AMOUNT TO WS-FORMATTED-AMOUNT.
    DISPLAY TRANSACTION-ID " - " TRANSACTION-TYPE " - " WS-FORMATTED-AMOUNT.
 
DEMONSTRATE-DUPLICATE-PROCESSING.
    DISPLAY " ".
    DISPLAY "Duplicate Key Processing Demonstration:".
    DISPLAY "======================================".
    
    DISPLAY "Processing all customers by ZIP code...".
    MOVE SPACES TO CUSTOMER-ZIP-CODE.
    START CUSTOMER-MASTER-FILE
        KEY IS GREATER THAN CUSTOMER-ZIP-CODE
        INVALID KEY
            DISPLAY "No customers found"
        NOT INVALID KEY
            PERFORM PROCESS-ALL-ZIP-CODES
    END-START.
 
PROCESS-ALL-ZIP-CODES.
    MOVE SPACES TO WS-SEARCH-ZIP.
    MOVE 0 TO WS-SEARCH-COUNT.
    
    PERFORM UNTIL CUSTOMER-EOF
        READ CUSTOMER-MASTER-FILE NEXT RECORD
        IF CUSTOMER-FILE-OK
            IF CUSTOMER-ZIP-CODE NOT = WS-SEARCH-ZIP
                IF WS-SEARCH-COUNT > 0
                    DISPLAY "ZIP " WS-SEARCH-ZIP ": " WS-SEARCH-COUNT " customers"
                END-IF
                MOVE CUSTOMER-ZIP-CODE TO WS-SEARCH-ZIP
                MOVE 1 TO WS-SEARCH-COUNT
            ELSE
                ADD 1 TO WS-SEARCH-COUNT
            END-IF
        END-IF
    END-PERFORM.
    
    IF WS-SEARCH-COUNT > 0
        DISPLAY "ZIP " WS-SEARCH-ZIP ": " WS-SEARCH-COUNT " customers"
    END-IF.
 
CLOSE-FILES.
    CLOSE CUSTOMER-MASTER-FILE.
    CLOSE TRANSACTION-FILE.

Best Practices and Guidelines

Recommended Practices

  • Design ALTERNATE keys based on actual query requirements
  • Use WITH DUPLICATES when multiple records may share key values
  • Create compound keys for complex search criteria
  • Consider performance impact of multiple alternate keys
  • Document all alternate key purposes and usage patterns
  • Test alternate key performance with realistic data volumes
  • Use meaningful field combinations for compound keys
  • Plan for future query requirements when designing keys

Common Pitfalls

  • Creating too many alternate keys affecting performance
  • Not using WITH DUPLICATES when needed
  • Poor compound key field ordering
  • Not handling duplicate key processing properly
  • Ignoring file status after START operations
  • Not testing with large data volumes
  • Creating keys that are rarely used
  • Not considering maintenance overhead of multiple keys

Related COBOL Concepts

  • INDEXED files - File organization supporting alternate keys
  • RECORD KEY - Primary key for indexed files
  • START statement - Positioning for alternate key access
  • READ NEXT - Sequential reading using alternate keys
  • WITH DUPLICATES - Allowing duplicate alternate key values
  • Compound keys - Multiple field alternate keys
  • File status - Error handling for key operations
  • DYNAMIC access - Combined sequential and random access