Overview
In this module, we will explore the integration of COBOL with DB2, a powerful relational database management system (RDBMS) from IBM. This combination is widely used in enterprise environments for handling large volumes of data efficiently. By the end of this module, you will understand how to embed SQL statements within COBOL programs to interact with DB2 databases.
Key Concepts
- DB2 Basics: Understanding what DB2 is and its role in data management.
- Embedded SQL: Learning how to embed SQL statements within COBOL programs.
- Connecting to DB2: Establishing a connection between COBOL programs and DB2 databases.
- Executing SQL Statements: Performing CRUD (Create, Read, Update, Delete) operations using SQL in COBOL.
- Handling SQL Errors: Managing errors that occur during SQL execution.
DB2 Basics
DB2 is a family of data management products, including database servers, developed by IBM. It is designed to store, retrieve, and manage data efficiently. DB2 supports SQL (Structured Query Language) for querying and manipulating data.
Key Features of DB2
- High Performance: Optimized for high-speed data processing.
- Scalability: Can handle large volumes of data and numerous concurrent users.
- Security: Provides robust security features to protect data.
- Reliability: Ensures data integrity and availability.
Embedded SQL in COBOL
Embedded SQL allows you to include SQL statements directly within your COBOL code. This integration enables COBOL programs to interact with DB2 databases seamlessly.
Basic Structure of Embedded SQL
- EXEC SQL: Marks the beginning of an SQL statement.
- SQL-STATEMENT: The SQL command to be executed.
- END-EXEC: Marks the end of the SQL statement.
Example: Simple SELECT Statement
EXEC SQL
SELECT FIRSTNAME, LASTNAME
INTO :FIRSTNAME, :LASTNAME
FROM EMPLOYEES
WHERE EMPLOYEE_ID = :EMP-ID
END-EXEC.- SELECT: SQL command to retrieve data.
- INTO: Specifies the COBOL variables to store the retrieved data.
- FROM: Specifies the table to query.
- WHERE: Specifies the condition to filter the data.
Connecting to DB2
To execute SQL statements, a COBOL program must first establish a connection to the DB2 database.
Steps to Connect to DB2
- Include SQLCA: SQL Communication Area (SQLCA) is a structure used to store information about the execution of SQL statements.
- Declare Host Variables: COBOL variables that will be used in SQL statements.
- Establish Connection: Use the
CONNECTstatement to connect to the DB2 database.
Example: Connecting to DB2
WORKING-STORAGE SECTION.
EXEC SQL INCLUDE SQLCA END-EXEC.
01 USERID PIC X(8) VALUE 'db2user'.
01 PASSWORD PIC X(8) VALUE 'db2pass'.
01 SQLCODE PIC S9(9) COMP.
PROCEDURE DIVISION.
EXEC SQL
CONNECT TO SAMPLE
USER :USERID USING :PASSWORD
END-EXEC.
IF SQLCODE NOT = 0
DISPLAY 'Connection failed with SQLCODE: ' SQLCODE
STOP RUN.
ELSE
DISPLAY 'Connection successful'.- SQLCA: Included to handle SQL execution information.
- USERID and PASSWORD: Host variables for database credentials.
- CONNECT: SQL command to establish a connection to the DB2 database.
Executing SQL Statements
Once connected, you can execute various SQL statements to interact with the database.
Example: Inserting Data
WORKING-STORAGE SECTION.
01 EMP-ID PIC 9(5).
01 FIRSTNAME PIC X(20).
01 LASTNAME PIC X(20).
PROCEDURE DIVISION.
MOVE 12345 TO EMP-ID.
MOVE 'John' TO FIRSTNAME.
MOVE 'Doe' TO LASTNAME.
EXEC SQL
INSERT INTO EMPLOYEES (EMPLOYEE_ID, FIRSTNAME, LASTNAME)
VALUES (:EMP-ID, :FIRSTNAME, :LASTNAME)
END-EXEC.
IF SQLCODE NOT = 0
DISPLAY 'Insert failed with SQLCODE: ' SQLCODE
STOP RUN.
ELSE
DISPLAY 'Insert successful'.- INSERT INTO: SQL command to insert data into a table.
- VALUES: Specifies the values to be inserted.
Handling SQL Errors
SQL errors can occur during the execution of SQL statements. These errors are captured in the SQLCA structure.
Common SQLCA Fields
- SQLCODE: Numeric code indicating the result of the SQL statement.
- SQLERRM: Error message text.
Example: Error Handling
EXEC SQL
DELETE FROM EMPLOYEES
WHERE EMPLOYEE_ID = :EMP-ID
END-EXEC.
IF SQLCODE NOT = 0
DISPLAY 'Delete failed with SQLCODE: ' SQLCODE
DISPLAY 'Error message: ' SQLERRM
STOP RUN.
ELSE
DISPLAY 'Delete successful'.- SQLCODE: Checked to determine if the SQL statement was successful.
- SQLERRM: Displays the error message if an error occurs.
Summary
In this module, we covered the basics of integrating COBOL with DB2, including:
- Understanding DB2 and its features.
- Embedding SQL statements within COBOL programs.
- Establishing a connection to a DB2 database.
- Executing SQL statements to perform database operations.
- Handling SQL errors effectively.
By mastering these concepts, you will be able to create robust COBOL programs that interact with DB2 databases, enabling efficient data management in enterprise environments.