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COBOL Tutorial

COBOL CHANGED Status Flag

The CHANGED status flag in COBOL is a powerful feature for detecting data modification in screen-based and interactive applications. This flag automatically tracks whether data fields have been modified by user input, enabling efficient screen processing, data validation, and selective field updates in forms-based applications where it's essential to identify which specific fields have been altered during user interaction, optimizing database performance and maintaining data integrity through targeted updates and comprehensive audit trails for regulatory compliance and business process automation.

Understanding CHANGED Flag

The CHANGED flag is automatically set by COBOL runtime when a field's value is modified through terminal input or screen operations. It provides a mechanism to detect which fields have been changed without manually comparing old and new values, enabling sophisticated screen processing workflows and optimized database operations in enterprise-scale applications.

Key Features:

  • Automatic modification detection for screen section fields and terminal I/O
  • Screen field change tracking with precise field-level granularity
  • Selective processing capabilities for performance optimization and efficiency
  • Form validation support with comprehensive field-level change awareness
  • Database update optimization through selective field modification detection
  • Integration with audit logging systems for compliance and change tracking
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*> Basic CHANGED flag usage with comprehensive change tracking
DATA DIVISION.
WORKING-STORAGE SECTION.
01  SCREEN-CONTROL-FLAGS.
    05  CUSTOMER-ID-CHANGED    PIC X VALUE 'N'.
        88  CUSTOMER-ID-MODIFIED   VALUE 'Y'.
    05  CUSTOMER-NAME-CHANGED  PIC X VALUE 'N'.
        88  CUSTOMER-NAME-MODIFIED VALUE 'Y'.
    05  CUSTOMER-PHONE-CHANGED PIC X VALUE 'N'.
        88  CUSTOMER-PHONE-MODIFIED VALUE 'Y'.
    05  CUSTOMER-EMAIL-CHANGED PIC X VALUE 'N'.
        88  CUSTOMER-EMAIL-MODIFIED VALUE 'Y'.
 
01  CUSTOMER-DATA.
    05  CUSTOMER-ID            PIC 9(8).
    05  CUSTOMER-NAME          PIC X(30).
    05  CUSTOMER-PHONE         PIC X(15).
    05  CUSTOMER-EMAIL         PIC X(40).
    05  CUSTOMER-STATUS        PIC X(10).
 
01  ORIGINAL-DATA.
    05  ORIG-CUSTOMER-ID       PIC 9(8).
    05  ORIG-CUSTOMER-NAME     PIC X(30).
    05  ORIG-CUSTOMER-PHONE    PIC X(15).
    05  ORIG-CUSTOMER-EMAIL    PIC X(40).
    05  ORIG-CUSTOMER-STATUS   PIC X(10).
 
01  CHANGE-STATISTICS.
    05  TOTAL-FIELDS-CHECKED   PIC 9(3) VALUE ZERO.
    05  FIELDS-CHANGED         PIC 9(3) VALUE ZERO.
    05  VALIDATION-PASSES      PIC 9(3) VALUE ZERO.
    05  VALIDATION-FAILURES    PIC 9(3) VALUE ZERO.
 
PROCEDURE DIVISION.
MAIN-SCREEN-PROCESSING.
    PERFORM INITIALIZE-SCREEN-DATA
    PERFORM DISPLAY-ENTRY-SCREEN
    PERFORM PROCESS-CHANGED-FIELDS
    PERFORM DISPLAY-CHANGE-SUMMARY.
 
INITIALIZE-SCREEN-DATA.
    MOVE CUSTOMER-DATA TO ORIGINAL-DATA
    MOVE 'N' TO CUSTOMER-ID-CHANGED
                CUSTOMER-NAME-CHANGED
                CUSTOMER-PHONE-CHANGED
                CUSTOMER-EMAIL-CHANGED
    MOVE ZERO TO TOTAL-FIELDS-CHECKED FIELDS-CHANGED
                 VALIDATION-PASSES VALIDATION-FAILURES.
 
PROCESS-CHANGED-FIELDS.
    ADD 1 TO TOTAL-FIELDS-CHECKED
    IF CUSTOMER-ID NOT = ORIG-CUSTOMER-ID
        MOVE 'Y' TO CUSTOMER-ID-CHANGED
        ADD 1 TO FIELDS-CHANGED
        DISPLAY "Customer ID changed: " ORIG-CUSTOMER-ID 
                " -> " CUSTOMER-ID
        PERFORM VALIDATE-CUSTOMER-ID
    END-IF
    
    ADD 1 TO TOTAL-FIELDS-CHECKED
    IF CUSTOMER-NAME NOT = ORIG-CUSTOMER-NAME
        MOVE 'Y' TO CUSTOMER-NAME-CHANGED
        ADD 1 TO FIELDS-CHANGED
        DISPLAY "Customer Name changed"
        PERFORM VALIDATE-CUSTOMER-NAME
    END-IF
    
    ADD 1 TO TOTAL-FIELDS-CHECKED
    IF CUSTOMER-PHONE NOT = ORIG-CUSTOMER-PHONE
        MOVE 'Y' TO CUSTOMER-PHONE-CHANGED
        ADD 1 TO FIELDS-CHANGED
        DISPLAY "Customer Phone changed"
        PERFORM VALIDATE-CUSTOMER-PHONE
    END-IF
    
    ADD 1 TO TOTAL-FIELDS-CHECKED
    IF CUSTOMER-EMAIL NOT = ORIG-CUSTOMER-EMAIL
        MOVE 'Y' TO CUSTOMER-EMAIL-CHANGED
        ADD 1 TO FIELDS-CHANGED
        DISPLAY "Customer Email changed"
        PERFORM VALIDATE-CUSTOMER-EMAIL
    END-IF.
 
VALIDATE-CUSTOMER-ID.
    IF CUSTOMER-ID = ZERO OR CUSTOMER-ID > 99999999
        ADD 1 TO VALIDATION-FAILURES
        DISPLAY "ERROR: Invalid Customer ID"
    ELSE
        ADD 1 TO VALIDATION-PASSES
        DISPLAY "Customer ID validation: PASSED"
    END-IF.
 
VALIDATE-CUSTOMER-NAME.
    IF CUSTOMER-NAME = SPACES
        ADD 1 TO VALIDATION-FAILURES
        DISPLAY "ERROR: Customer Name cannot be blank"
    ELSE
        ADD 1 TO VALIDATION-PASSES
        DISPLAY "Customer Name validation: PASSED"
    END-IF.
 
VALIDATE-CUSTOMER-PHONE.
    IF CUSTOMER-PHONE = SPACES
        ADD 1 TO VALIDATION-FAILURES
        DISPLAY "ERROR: Phone number required"
    ELSE
        ADD 1 TO VALIDATION-PASSES
        DISPLAY "Phone validation: PASSED"
    END-IF.
 
VALIDATE-CUSTOMER-EMAIL.
    IF CUSTOMER-EMAIL = SPACES
        ADD 1 TO VALIDATION-FAILURES
        DISPLAY "ERROR: Email address required"
    ELSE
        ADD 1 TO VALIDATION-PASSES
        DISPLAY "Email validation: PASSED"
    END-IF.
 
DISPLAY-CHANGE-SUMMARY.
    DISPLAY "=== Change Processing Summary ==="
    DISPLAY "Total Fields Checked: " TOTAL-FIELDS-CHECKED
    DISPLAY "Fields Changed: " FIELDS-CHANGED
    DISPLAY "Validations Passed: " VALIDATION-PASSES
    DISPLAY "Validation Failures: " VALIDATION-FAILURES.

Advanced Screen Processing with CHANGED

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*> Advanced screen processing using CHANGED flag for complex forms
DATA DIVISION.
WORKING-STORAGE SECTION.
01  SCREEN-CONTROL-SYSTEM.
    05  TOTAL-FIELDS       PIC 9(3) VALUE 15.
    05  CHANGED-FIELDS     PIC 9(3) VALUE ZERO.
    05  VALIDATION-ERRORS  PIC 9(3) VALUE ZERO.
    05  SCREEN-STATUS      PIC X(10) VALUE "READY".
        88  SCREEN-READY   VALUE "READY".
        88  SCREEN-CHANGED VALUE "CHANGED".
        88  SCREEN-ERROR   VALUE "ERROR".
 
01  FIELD-CHANGE-TRACKING.
    05  FIELD-CHANGES      OCCURS 15 TIMES.
        10  FC-FIELD-NAME  PIC X(20).
        10  FC-OLD-VALUE   PIC X(50).
        10  FC-NEW-VALUE   PIC X(50).
        10  FC-CHANGED     PIC X VALUE 'N'.
            88  FIELD-WAS-CHANGED VALUE 'Y'.
        10  FC-VALIDATED   PIC X VALUE 'N'.
            88  FIELD-IS-VALID VALUE 'Y'.
        10  FC-TIMESTAMP   PIC X(26).
        10  FC-USER-ID     PIC X(8).
 
01  CUSTOMER-SCREEN-DATA.
    05  CUST-ID            PIC 9(8).
    05  CUST-NAME          PIC X(30).
    05  CUST-ADDRESS       PIC X(50).
    05  CUST-PHONE         PIC X(15).
    05  CUST-EMAIL         PIC X(40).
    05  CUST-STATUS        PIC X(10).
    05  CUST-CREDIT-LIMIT  PIC 9(7)V99.
    05  CUST-DISCOUNT-PCT  PIC 9(2)V99.
 
01  ORIGINAL-SCREEN-DATA.
    05  ORIG-CUST-ID       PIC 9(8).
    05  ORIG-CUST-NAME     PIC X(30).
    05  ORIG-CUST-ADDRESS  PIC X(50).
    05  ORIG-CUST-PHONE    PIC X(15).
    05  ORIG-CUST-EMAIL    PIC X(40).
    05  ORIG-CUST-STATUS   PIC X(10).
    05  ORIG-CUST-CREDIT-LIMIT PIC 9(7)V99.
    05  ORIG-CUST-DISCOUNT-PCT PIC 9(2)V99.
 
01  VALIDATION-RULES.
    05  MIN-CREDIT-LIMIT   PIC 9(7)V99 VALUE 100.00.
    05  MAX-CREDIT-LIMIT   PIC 9(7)V99 VALUE 999999.99.
    05  MAX-DISCOUNT-PCT   PIC 9(2)V99 VALUE 50.00.
 
PROCEDURE DIVISION.
ADVANCED-SCREEN-PROCESSING.
    PERFORM INITIALIZE-SCREEN-SYSTEM
    PERFORM DISPLAY-CUSTOMER-SCREEN
    PERFORM PROCESS-SCREEN-CHANGES
    PERFORM VALIDATE-CHANGED-FIELDS
    PERFORM UPDATE-CHANGED-DATA.
 
INITIALIZE-SCREEN-SYSTEM.
    MOVE ZERO TO CHANGED-FIELDS VALIDATION-ERRORS
    MOVE "READY" TO SCREEN-STATUS
    MOVE CUSTOMER-SCREEN-DATA TO ORIGINAL-SCREEN-DATA
    MOVE FUNCTION CURRENT-DATE TO WS-CURRENT-TIMESTAMP
    
    *> Initialize field tracking
    PERFORM VARYING WS-I FROM 1 BY 1 UNTIL WS-I > TOTAL-FIELDS
        MOVE 'N' TO FC-CHANGED(WS-I) FC-VALIDATED(WS-I)
        MOVE SPACES TO FC-FIELD-NAME(WS-I) FC-OLD-VALUE(WS-I) 
                       FC-NEW-VALUE(WS-I) FC-USER-ID(WS-I)
        MOVE SPACES TO FC-TIMESTAMP(WS-I)
    END-PERFORM.
 
PROCESS-SCREEN-CHANGES.
    MOVE ZERO TO CHANGED-FIELDS
    
    *> Check each field for changes
    PERFORM CHECK-CUSTOMER-ID-CHANGE
    PERFORM CHECK-CUSTOMER-NAME-CHANGE
    PERFORM CHECK-CUSTOMER-ADDRESS-CHANGE
    PERFORM CHECK-CUSTOMER-PHONE-CHANGE
    PERFORM CHECK-CUSTOMER-EMAIL-CHANGE
    PERFORM CHECK-CUSTOMER-STATUS-CHANGE
    PERFORM CHECK-CREDIT-LIMIT-CHANGE
    PERFORM CHECK-DISCOUNT-PCT-CHANGE
    
    IF CHANGED-FIELDS > ZERO
        MOVE "CHANGED" TO SCREEN-STATUS
        DISPLAY "Screen contains " CHANGED-FIELDS " changed fields"
    ELSE
        DISPLAY "No changes detected on screen"
    END-IF.
 
CHECK-CUSTOMER-ID-CHANGE.
    IF CUST-ID NOT = ORIG-CUST-ID
        ADD 1 TO CHANGED-FIELDS
        MOVE "CUSTOMER_ID" TO FC-FIELD-NAME(1)
        MOVE ORIG-CUST-ID TO FC-OLD-VALUE(1)
        MOVE CUST-ID TO FC-NEW-VALUE(1)
        MOVE 'Y' TO FC-CHANGED(1)
        MOVE WS-CURRENT-TIMESTAMP TO FC-TIMESTAMP(1)
        MOVE WS-USER-ID TO FC-USER-ID(1)
        DISPLAY "Customer ID changed: " ORIG-CUST-ID " -> " CUST-ID
    END-IF.
 
CHECK-CUSTOMER-NAME-CHANGE.
    IF CUST-NAME NOT = ORIG-CUST-NAME
        ADD 1 TO CHANGED-FIELDS
        MOVE "CUSTOMER_NAME" TO FC-FIELD-NAME(2)
        MOVE ORIG-CUST-NAME TO FC-OLD-VALUE(2)
        MOVE CUST-NAME TO FC-NEW-VALUE(2)
        MOVE 'Y' TO FC-CHANGED(2)
        MOVE WS-CURRENT-TIMESTAMP TO FC-TIMESTAMP(2)
        MOVE WS-USER-ID TO FC-USER-ID(2)
        DISPLAY "Customer Name changed"
    END-IF.
 
CHECK-CREDIT-LIMIT-CHANGE.
    IF CUST-CREDIT-LIMIT NOT = ORIG-CUST-CREDIT-LIMIT
        ADD 1 TO CHANGED-FIELDS
        MOVE "CREDIT_LIMIT" TO FC-FIELD-NAME(7)
        MOVE ORIG-CUST-CREDIT-LIMIT TO FC-OLD-VALUE(7)
        MOVE CUST-CREDIT-LIMIT TO FC-NEW-VALUE(7)
        MOVE 'Y' TO FC-CHANGED(7)
        MOVE WS-CURRENT-TIMESTAMP TO FC-TIMESTAMP(7)
        MOVE WS-USER-ID TO FC-USER-ID(7)
        DISPLAY "Credit Limit changed"
    END-IF.
 
CHECK-DISCOUNT-PCT-CHANGE.
    IF CUST-DISCOUNT-PCT NOT = ORIG-CUST-DISCOUNT-PCT
        ADD 1 TO CHANGED-FIELDS
        MOVE "DISCOUNT_PCT" TO FC-FIELD-NAME(8)
        MOVE ORIG-CUST-DISCOUNT-PCT TO FC-OLD-VALUE(8)
        MOVE CUST-DISCOUNT-PCT TO FC-NEW-VALUE(8)
        MOVE 'Y' TO FC-CHANGED(8)
        MOVE WS-CURRENT-TIMESTAMP TO FC-TIMESTAMP(8)
        MOVE WS-USER-ID TO FC-USER-ID(8)
        DISPLAY "Discount Percentage changed"
    END-IF.
 
VALIDATE-CHANGED-FIELDS.
    MOVE ZERO TO VALIDATION-ERRORS
    
    PERFORM VARYING WS-I FROM 1 BY 1 UNTIL WS-I > 8
        IF FC-CHANGED(WS-I) = 'Y'
            PERFORM VALIDATE-FIELD-CHANGE
        END-IF
    END-PERFORM
    
    IF VALIDATION-ERRORS > ZERO
        MOVE "ERROR" TO SCREEN-STATUS
        DISPLAY "Validation errors found: " VALIDATION-ERRORS
    END-IF.
 
VALIDATE-FIELD-CHANGE.
    EVALUATE FC-FIELD-NAME(WS-I)
        WHEN "CUSTOMER_ID"
            PERFORM VALIDATE-CUSTOMER-ID-FIELD
        WHEN "CUSTOMER_NAME"
            PERFORM VALIDATE-CUSTOMER-NAME-FIELD
        WHEN "CUSTOMER_ADDRESS"
            PERFORM VALIDATE-CUSTOMER-ADDRESS-FIELD
        WHEN "CUSTOMER_PHONE"
            PERFORM VALIDATE-CUSTOMER-PHONE-FIELD
        WHEN "CUSTOMER_EMAIL"
            PERFORM VALIDATE-CUSTOMER-EMAIL-FIELD
        WHEN "CUSTOMER_STATUS"
            PERFORM VALIDATE-CUSTOMER-STATUS-FIELD
        WHEN "CREDIT_LIMIT"
            PERFORM VALIDATE-CREDIT-LIMIT-FIELD
        WHEN "DISCOUNT_PCT"
            PERFORM VALIDATE-DISCOUNT-PCT-FIELD
    END-EVALUATE.
 
VALIDATE-CREDIT-LIMIT-FIELD.
    IF CUST-CREDIT-LIMIT < MIN-CREDIT-LIMIT OR
       CUST-CREDIT-LIMIT > MAX-CREDIT-LIMIT
        ADD 1 TO VALIDATION-ERRORS
        DISPLAY "Credit limit must be between " 
                MIN-CREDIT-LIMIT " and " MAX-CREDIT-LIMIT
    ELSE
        MOVE 'Y' TO FC-VALIDATED(WS-I)
    END-IF.
 
VALIDATE-DISCOUNT-PCT-FIELD.
    IF CUST-DISCOUNT-PCT < ZERO OR
       CUST-DISCOUNT-PCT > MAX-DISCOUNT-PCT
        ADD 1 TO VALIDATION-ERRORS
        DISPLAY "Discount percentage must be between 0 and " 
                MAX-DISCOUNT-PCT "%"
    ELSE
        MOVE 'Y' TO FC-VALIDATED(WS-I)
    END-IF.
 
UPDATE-CHANGED-DATA.
    IF SCREEN-STATUS = "CHANGED" AND VALIDATION-ERRORS = ZERO
        PERFORM UPDATE-DATABASE-RECORDS
        PERFORM LOG-FIELD-CHANGES
        PERFORM RESET-CHANGE-FLAGS
        DISPLAY "Update completed successfully"
    ELSE
        DISPLAY "Update cancelled due to validation errors"
    END-IF.
 
LOG-FIELD-CHANGES.
    DISPLAY "=== Detailed Change Log ==="
    PERFORM VARYING WS-I FROM 1 BY 1 UNTIL WS-I > 8
        IF FC-CHANGED(WS-I) = 'Y'
            DISPLAY "Field: " FC-FIELD-NAME(WS-I)
            DISPLAY "User: " FC-USER-ID(WS-I)
            DISPLAY "Old Value: " FC-OLD-VALUE(WS-I)
            DISPLAY "New Value: " FC-NEW-VALUE(WS-I)
            DISPLAY "Timestamp: " FC-TIMESTAMP(WS-I)
            DISPLAY "Validated: " FC-VALIDATED(WS-I)
            DISPLAY "---"
        END-IF
    END-PERFORM.
 
RESET-CHANGE-FLAGS.
    *> Reset for next screen operation
    MOVE CUSTOMER-SCREEN-DATA TO ORIGINAL-SCREEN-DATA
    PERFORM VARYING WS-I FROM 1 BY 1 UNTIL WS-I > 8
        MOVE 'N' TO FC-CHANGED(WS-I) FC-VALIDATED(WS-I)
    END-PERFORM
    MOVE "READY" TO SCREEN-STATUS.

Database Integration with Change Detection

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*> Database integration using CHANGED flag for selective updates
DATA DIVISION.
WORKING-STORAGE SECTION.
01  DATABASE-UPDATE-CONTROL.
    05  UPDATE-COUNT       PIC 9(4) VALUE ZERO.
    05  INSERT-COUNT       PIC 9(4) VALUE ZERO.
    05  ERROR-COUNT        PIC 9(3) VALUE ZERO.
    05  TRANSACTION-STATUS PIC X(10) VALUE "PENDING".
        88  TRANS-PENDING  VALUE "PENDING".
        88  TRANS-COMMITTED VALUE "COMMITTED".
        88  TRANS-ROLLEDBACK VALUE "ROLLEDBACK".
 
01  SQL-STATEMENTS.
    05  UPDATE-CUSTOMER-SQL PIC X(200) VALUE
        "UPDATE CUSTOMERS SET ".
    05  WHERE-CLAUSE       PIC X(50) VALUE
        " WHERE CUSTOMER_ID = ?".
    05  DYNAMIC-SQL        PIC X(500).
 
01  CHANGE-AUDIT-LOG.
    05  AUDIT-RECORD.
        10  AUDIT-USER-ID  PIC X(8).
        10  AUDIT-TABLE    PIC X(20).
        10  AUDIT-FIELD    PIC X(20).
        10  AUDIT-OLD-VAL  PIC X(50).
        10  AUDIT-NEW-VAL  PIC X(50).
        10  AUDIT-TIMESTAMP PIC X(26).
        10  AUDIT-ACTION   PIC X(10).
 
01  PERFORMANCE-METRICS.
    05  SELECTIVE-UPDATES  PIC 9(6) VALUE ZERO.
    05  FULL-UPDATES       PIC 9(6) VALUE ZERO.
    05  UPDATE-TIME-START  PIC 9(8).
    05  UPDATE-TIME-END    PIC 9(8).
    05  UPDATE-DURATION    PIC 9(4)V99.
 
PROCEDURE DIVISION.
DATABASE-INTEGRATION-PROCESSING.
    PERFORM INITIALIZE-DATABASE-UPDATE
    PERFORM BUILD-SELECTIVE-UPDATE-SQL
    PERFORM EXECUTE-DATABASE-UPDATES
    PERFORM COMMIT-OR-ROLLBACK-TRANSACTION
    PERFORM DISPLAY-PERFORMANCE-METRICS.
 
INITIALIZE-DATABASE-UPDATE.
    MOVE ZERO TO UPDATE-COUNT INSERT-COUNT ERROR-COUNT
                 SELECTIVE-UPDATES FULL-UPDATES
    MOVE "PENDING" TO TRANSACTION-STATUS
    MOVE FUNCTION CURRENT-DATE TO AUDIT-TIMESTAMP
    MOVE WS-USER-ID TO AUDIT-USER-ID
    MOVE "CUSTOMERS" TO AUDIT-TABLE
    MOVE FUNCTION CURRENT-DATE(9:8) TO UPDATE-TIME-START.
 
BUILD-SELECTIVE-UPDATE-SQL.
    MOVE SPACES TO DYNAMIC-SQL
    STRING "UPDATE CUSTOMERS SET " DELIMITED BY SIZE
        INTO DYNAMIC-SQL
    END-STRING
    
    MOVE 'N' TO WS-FIRST-FIELD
    
    *> Build SQL for changed fields only
    PERFORM VARYING WS-I FROM 1 BY 1 UNTIL WS-I > 8
        IF FC-CHANGED(WS-I) = 'Y' AND FC-VALIDATED(WS-I) = 'Y'
            PERFORM ADD-FIELD-TO-UPDATE-SQL
        END-IF
    END-PERFORM
    
    *> Add WHERE clause
    STRING DYNAMIC-SQL DELIMITED BY "  "
           WHERE-CLAUSE DELIMITED BY SIZE
        INTO DYNAMIC-SQL
    END-STRING
    
    DISPLAY "Generated Selective SQL: " DYNAMIC-SQL.
 
ADD-FIELD-TO-UPDATE-SQL.
    IF WS-FIRST-FIELD = 'Y'
        STRING DYNAMIC-SQL DELIMITED BY "  "
               ", " DELIMITED BY SIZE
            INTO DYNAMIC-SQL
        END-STRING
    ELSE
        MOVE 'Y' TO WS-FIRST-FIELD
    END-IF
    
    EVALUATE FC-FIELD-NAME(WS-I)
        WHEN "CUSTOMER_NAME"
            STRING DYNAMIC-SQL DELIMITED BY "  "
                   "CUSTOMER_NAME = ?" DELIMITED BY SIZE
                INTO DYNAMIC-SQL
            END-STRING
        WHEN "CUSTOMER_ADDRESS"
            STRING DYNAMIC-SQL DELIMITED BY "  "
                   "CUSTOMER_ADDRESS = ?" DELIMITED BY SIZE
                INTO DYNAMIC-SQL
            END-STRING
        WHEN "CUSTOMER_PHONE"
            STRING DYNAMIC-SQL DELIMITED BY "  "
                   "CUSTOMER_PHONE = ?" DELIMITED BY SIZE
                INTO DYNAMIC-SQL
            END-STRING
        WHEN "CUSTOMER_EMAIL"
            STRING DYNAMIC-SQL DELIMITED BY "  "
                   "CUSTOMER_EMAIL = ?" DELIMITED BY SIZE
                INTO DYNAMIC-SQL
            END-STRING
        WHEN "CUSTOMER_STATUS"
            STRING DYNAMIC-SQL DELIMITED BY "  "
                   "CUSTOMER_STATUS = ?" DELIMITED BY SIZE
                INTO DYNAMIC-SQL
            END-STRING
        WHEN "CREDIT_LIMIT"
            STRING DYNAMIC-SQL DELIMITED BY "  "
                   "CREDIT_LIMIT = ?" DELIMITED BY SIZE
                INTO DYNAMIC-SQL
            END-STRING
        WHEN "DISCOUNT_PCT"
            STRING DYNAMIC-SQL DELIMITED BY "  "
                   "DISCOUNT_PCT = ?" DELIMITED BY SIZE
                INTO DYNAMIC-SQL
            END-STRING
    END-EVALUATE.
 
EXECUTE-DATABASE-UPDATES.
    *> Execute the selective update
    EXEC SQL
        PREPARE UPDATE_STMT FROM :DYNAMIC-SQL
    END-EXEC
    
    IF SQLCODE = 0
        PERFORM BIND-CHANGED-VALUES
        EXEC SQL
            EXECUTE UPDATE_STMT
        END-EXEC
        
        IF SQLCODE = 0
            ADD 1 TO UPDATE-COUNT
            ADD 1 TO SELECTIVE-UPDATES
            PERFORM LOG-UPDATE-SUCCESS
        ELSE
            ADD 1 TO ERROR-COUNT
            PERFORM LOG-UPDATE-ERROR
        END-IF
    ELSE
        ADD 1 TO ERROR-COUNT
        DISPLAY "SQL Prepare Error: " SQLCODE
    END-IF.
 
BIND-CHANGED-VALUES.
    MOVE 1 TO WS-PARAM-NUM
    
    PERFORM VARYING WS-I FROM 1 BY 1 UNTIL WS-I > 8
        IF FC-CHANGED(WS-I) = 'Y' AND FC-VALIDATED(WS-I) = 'Y'
            PERFORM BIND-PARAMETER-VALUE
        END-IF
    END-PERFORM
    
    *> Bind customer ID for WHERE clause
    EXEC SQL
        SET :CUST-ID = PARAMETER :WS-PARAM-NUM
    END-EXEC.
 
BIND-PARAMETER-VALUE.
    EVALUATE FC-FIELD-NAME(WS-I)
        WHEN "CUSTOMER_NAME"
            EXEC SQL
                SET :CUST-NAME = PARAMETER :WS-PARAM-NUM
            END-EXEC
        WHEN "CUSTOMER_ADDRESS"
            EXEC SQL
                SET :CUST-ADDRESS = PARAMETER :WS-PARAM-NUM
            END-EXEC
        WHEN "CUSTOMER_PHONE"
            EXEC SQL
                SET :CUST-PHONE = PARAMETER :WS-PARAM-NUM
            END-EXEC
        WHEN "CUSTOMER_EMAIL"
            EXEC SQL
                SET :CUST-EMAIL = PARAMETER :WS-PARAM-NUM
            END-EXEC
        WHEN "CUSTOMER_STATUS"
            EXEC SQL
                SET :CUST-STATUS = PARAMETER :WS-PARAM-NUM
            END-EXEC
        WHEN "CREDIT_LIMIT"
            EXEC SQL
                SET :CUST-CREDIT-LIMIT = PARAMETER :WS-PARAM-NUM
            END-EXEC
        WHEN "DISCOUNT_PCT"
            EXEC SQL
                SET :CUST-DISCOUNT-PCT = PARAMETER :WS-PARAM-NUM
            END-EXEC
    END-EVALUATE
    
    ADD 1 TO WS-PARAM-NUM.
 
LOG-UPDATE-SUCCESS.
    PERFORM VARYING WS-I FROM 1 BY 1 UNTIL WS-I > 8
        IF FC-CHANGED(WS-I) = 'Y'
            MOVE FC-FIELD-NAME(WS-I) TO AUDIT-FIELD
            MOVE FC-OLD-VALUE(WS-I) TO AUDIT-OLD-VAL
            MOVE FC-NEW-VALUE(WS-I) TO AUDIT-NEW-VAL
            MOVE "UPDATE" TO AUDIT-ACTION
            PERFORM WRITE-AUDIT-RECORD
        END-IF
    END-PERFORM.
 
COMMIT-OR-ROLLBACK-TRANSACTION.
    MOVE FUNCTION CURRENT-DATE(9:8) TO UPDATE-TIME-END
    COMPUTE UPDATE-DURATION = UPDATE-TIME-END - UPDATE-TIME-START
    
    IF ERROR-COUNT = ZERO
        EXEC SQL COMMIT END-EXEC
        MOVE "COMMITTED" TO TRANSACTION-STATUS
        DISPLAY "Transaction committed successfully"
        DISPLAY "Updated records: " UPDATE-COUNT
    ELSE
        EXEC SQL ROLLBACK END-EXEC
        MOVE "ROLLEDBACK" TO TRANSACTION-STATUS
        DISPLAY "Transaction rolled back due to errors"
        DISPLAY "Error count: " ERROR-COUNT
    END-IF.
 
DISPLAY-PERFORMANCE-METRICS.
    DISPLAY "=== Database Update Performance ==="
    DISPLAY "Selective Updates: " SELECTIVE-UPDATES
    DISPLAY "Full Table Updates: " FULL-UPDATES
    DISPLAY "Update Duration: " UPDATE-DURATION " seconds"
    DISPLAY "Transaction Status: " TRANSACTION-STATUS
    
    IF SELECTIVE-UPDATES > 0
        DISPLAY "Performance Optimization: ENABLED"
        DISPLAY "Changed Fields Only: YES"
    ELSE
        DISPLAY "Performance Optimization: DISABLED"
        DISPLAY "Full Record Updates: YES"
    END-IF.

Best Practices and Guidelines

CHANGED Flag Implementation Guidelines:

  • Initialize change flags consistently before screen operations to ensure accurate tracking
  • Use selective processing for changed fields only to optimize database performance
  • Implement comprehensive validation for field changes before database updates
  • Log field changes for audit purposes and compliance requirements
  • Reset flags after successful updates to prepare for subsequent screen operations
  • Handle transaction boundaries carefully when multiple fields are changed
  • Implement rollback mechanisms for partial update failures
  • Use change timestamps for concurrency control and audit trails
  • Consider field-level security when processing changed data
  • Optimize screen refresh by updating only changed display areas
  • Monitor performance metrics to measure optimization effectiveness
  • Implement proper error handling for failed change detection operations

Comprehensive FAQ

Q: Does CHANGED work with all field types?

CHANGED status is primarily designed for screen section fields and terminal I/O operations. It works with alphanumeric, numeric, and edited fields in screen processing contexts. For Working-Storage fields, you need to implement manual change detection by comparing current values with saved original values using string comparison or arithmetic operations.

Q: How do I reset the CHANGED flag after processing?

The CHANGED flag is automatically reset when you redisplay the screen or field. You can also manually reset it by moving the current field values to your "original values" storage area after successful processing. This prepares the system for detecting the next set of changes and ensures accurate change tracking for subsequent operations.

Q: Can CHANGED detect partial field modifications?

Yes, CHANGED detects any modification to a field, whether it's a complete replacement or partial changes. Even changing a single character in a field will trigger the CHANGED status. However, it doesn't provide information about what specifically changed within the field - you need additional logic to determine the exact changes.

Q: How does CHANGED work with database transactions?

CHANGED flag detection should be used to build selective UPDATE statements that only modify fields that have actually changed. This improves performance and reduces database locking. Always validate changed fields before committing transactions and implement proper rollback handling for failed updates to maintain data consistency.

Q: What's the best way to handle multiple changed fields?

Process all changed fields within a single transaction boundary when possible. Validate all fields first, then perform all updates together. If one update fails, roll back the entire transaction to maintain data consistency. Use field-level timestamps for audit trails and concurrency control in multi-user environments.

Q: Can I use CHANGED for performance optimization?

Absolutely! CHANGED enables significant performance optimizations by allowing selective processing. Only validate, transform, and update fields that have actually changed. This reduces CPU usage, database I/O, and network traffic in forms-based applications with many fields, especially in high-volume transaction processing environments.

Q: How do I implement audit trails with CHANGED flags?

Create audit log records for each changed field, capturing the old value, new value, timestamp, user ID, and field name. Store this information in audit tables for compliance reporting and change tracking. Include transaction IDs to group related changes and implement retention policies for audit data management.

Interactive Quiz

Test Your CHANGED Flag Knowledge

1. What is the primary purpose of the CHANGED flag?

2. When is the CHANGED flag automatically reset?

3. What's the main benefit of using CHANGED for database updates?

Answers: 1-B, 2-B, 3-B