How to use dclgen in cobol programmer

COBOL - Database Interface



As of now, we have learned the use of files in COBOL. Now, we will discuss how a COBOL program interacts with DB2. It involves the following terms -

  • Embedded SQL
  • DB2 application programming
  • Host variables
  • SQLCA
  • SQL queries
  • Cursors

Embedded SQL

Embedded SQL statements are used in COBOL programs to perform standard SQL operations. Embedded SQL statements are preprocessed by the SQL processor before the application program is compiled. COBOL is known as the Host Language. COBOL-DB2 applications are those applications that include both COBOL and DB2.

Embedded SQL statements work like normal SQL statements with some minor changes. For example, the output of a query is directed to a predefined set of variables which are referred as Host variables. An additional INTO clause is placed in the SELECT statement.

DB2 application programming

Following are rules to be followed while coding a COBOL-DB2 program -

  • All the SQL statements must be delimited between EXEC SQL other ENDEXEC..

  • SQL statements must be coded in Area B.

  • All the tables that are used in a program must be declared in the Working Storage Section. This is done by using the INCLUDE statement.

  • All SQL statements other than INCLUDE and DECLARE TABLE must appear in the Procedure Division.

Host variables

Host variables are used for receiving data from a table or inserting data in a table. Host variables must be declared for all values ‚Äč‚Äčthat are to be passed between the program and the DB2. They are declared in the Working Storage Section.

Host variables cannot be group items, but they may be grouped together in host structure. They cannot be Renamed or Redefined. Using host variables with SQL statements, prefix them with a colon (:)..

syntax

Following is the syntax to declare host variables and include tables in the Working-Storage section -

DATA DIVISION. WORKING STORAGE SECTION. EXEC SQL INCLUDE table-name END-EXEC. EXEC SQL BEGIN DECLARE SECTION END-EXEC. 01 STUDENT REC. 05 STUDENT ID PIC 9 (4). 05 STUDENT NAME PIC X (25). 05 STUDENT ADDRESS X (50). EXEC SQL END DECLARE SECTION END-EXEC.

SQLCA

SQLCA is a SQL communication area through which DB2 passes the feedback of SQL execution to the program. It tells the program whether an execution was successful or not. There are a number of predefined variables under SQLCA like SQLCODE which contains the error code. The value '000' in SQLCODE states a successful execution.

syntax

Following is the syntax to declare an SQLCA in the Working-Storage section -

DATA DIVISION. WORKING STORAGE SECTION. EXEC SQL INCLUDE SQLCA END-EXEC.

SQL queries

Let's assume we have one table named as 'Student' that contains Student-Id, Student-Name, and Student-Address.

The STUDENT table contains the following data -

Student Id Student Name Student Address 1001 Mohtashim M. Hyderabad 1002 Nishant Malik Delhi 1003 Amitabh Bachan Mumbai 1004 Chulbul Pandey Lucknow

The following example shows the usage of SELECT query in a COBOL program -

IDENTIFICATION DIVISION. PROGRAM ID. HELLO. DATA DIVISION. WORKING STORAGE SECTION. EXEC SQL INCLUDE SQLCA END-EXEC. EXEC SQL INCLUDE STUDENT END-EXEC. EXEC SQL BEGIN DECLARE SECTION END-EXEC. 01 WS-STUDENT-REC. 05 WS-STUDENT-ID PIC 9 (4). 05 WS STUDENT NAME PIC X (25). 05 WS-STUDENT-ADDRESS X (50). EXEC SQL END DECLARE SECTION END-EXEC. PROCEDURE DIVISION. EXEC SQL SELECT STUDENT-ID, STUDENT-NAME, STUDENT-ADDRESS INTO: WS-STUDENT-ID,: WS-STUDENT-NAME, WS-STUDENT-ADDRESS FROM STUDENT WHERE STUDENT-ID = 1004 END-EXEC. IF SQLCODE = 0 DISPLAY WS-STUDENT-RECORD ELSE DISPLAY 'Error' END-IF. STOP RUN.

JCL to execute the above COBOL program -

// SAMPLE JOB (TESTJCL, XXXXXX), CLASS = A, MSGCLASS = C // STEP001 EXEC PGM = IKJEFT01 // STEPLIB DD DSN = MYDATA.URMI.DBRMLIB, DISP = SHR // SYSPRINT DD SYSOUT = * // SYSUDUMP DD SYSOUT = * // SYSOUT DD SYSOUT = * // SYSTSIN DD * DSN SYSTEM (SSID) RUN PROGRAM (HELLO) PLAN (PLANNAME) - END / *

When you compile and execute the above program, it produces the following result -

1004 Chulbul Pandey Lucknow

The following example shows the usage of INSERT query in a COBOL program -

IDENTIFICATION DIVISION. PROGRAM ID. HELLO. DATA DIVISION. WORKING STORAGE SECTION. EXEC SQL INCLUDE SQLCA END-EXEC. EXEC SQL INCLUDE STUDENT END-EXEC. EXEC SQL BEGIN DECLARE SECTION END-EXEC. 01 WS-STUDENT-REC. 05 WS-STUDENT-ID PIC 9 (4). 05 WS STUDENT NAME PIC X (25). 05 WS-STUDENT-ADDRESS X (50). EXEC SQL END DECLARE SECTION END-EXEC. PROCEDURE DIVISION. MOVE 1005 TO WS-STUDENT-ID. MOVE 'TutorialsPoint' TO WS-STUDENT-NAME. MOVE 'Hyderabad' TO WS-STUDENT-ADDRESS. EXEC SQL INSERT INTO STUDENT (STUDENT-ID, STUDENT-NAME, STUDENT-ADDRESS) VALUES (: WS-STUDENT-ID,: WS-STUDENT-NAME, WS-STUDENT-ADDRESS) END-EXEC. IF SQLCODE = 0 DISPLAY 'Record Inserted Successfully' DISPLAY WS-STUDENT-REC ELSE DISPLAY 'Error' END-IF. STOP RUN.

JCL to execute the above COBOL program -

// SAMPLE JOB (TESTJCL, XXXXXX), CLASS = A, MSGCLASS = C // STEP001 EXEC PGM = IKJEFT01 // STEPLIB DD DSN = MYDATA.URMI.DBRMLIB, DISP = SHR // SYSPRINT DD SYSOUT = * // SYSUDUMP DD SYSOUT = * // SYSOUT DD SYSOUT = * // SYSTSIN DD * DSN SYSTEM (SSID) RUN PROGRAM (HELLO) PLAN (PLANNAME) - END / *

When you compile and execute the above program, it produces the following result -

Record Inserted Successfully 1005 TutorialsPoint Hyderabad

The following example shows the usage of UPDATE query in a COBOL program -

IDENTIFICATION DIVISION. PROGRAM ID. HELLO. DATA DIVISION. WORKING STORAGE SECTION. EXEC SQL INCLUDE SQLCA END-EXEC. EXEC SQL INCLUDE STUDENT END-EXEC. EXEC SQL BEGIN DECLARE SECTION END-EXEC. 01 WS-STUDENT-REC. 05 WS-STUDENT-ID PIC 9 (4). 05 WS STUDENT NAME PIC X (25). 05 WS-STUDENT-ADDRESS X (50). EXEC SQL END DECLARE SECTION END-EXEC. PROCEDURE DIVISION. MOVE 'Bangalore' TO WS-STUDENT-ADDRESS. EXEC SQL UPDATE STUDENT SET STUDENT-ADDRESS =: WS-STUDENT-ADDRESS WHERE STUDENT-ID = 1003 END-EXEC. IF SQLCODE = 0 DISPLAY 'Record Updated Successfully' ELSE DISPLAY 'Error' END-IF. STOP RUN.

JCL to execute the above COBOL program -

// SAMPLE JOB (TESTJCL, XXXXXX), CLASS = A, MSGCLASS = C // STEP001 EXEC PGM = IKJEFT01 // STEPLIB DD DSN = MYDATA.URMI.DBRMLIB, DISP = SHR // SYSPRINT DD SYSOUT = * // SYSUDUMP DD SYSOUT = * // SYSOUT DD SYSOUT = * // SYSTSIN DD * DSN SYSTEM (SSID) RUN PROGRAM (HELLO) PLAN (PLANNAME) - END / *

When you compile and execute the above program, it produces the following result -

Record Updated Successfully

The following example shows the usage of DELETE query in a COBOL program -

IDENTIFICATION DIVISION. PROGRAM ID. HELLO. DATA DIVISION. WORKING STORAGE SECTION. EXEC SQL INCLUDE SQLCA END-EXEC. EXEC SQL INCLUDE STUDENT END-EXEC. EXEC SQL BEGIN DECLARE SECTION END-EXEC. 01 WS-STUDENT-REC. 05 WS-STUDENT-ID PIC 9 (4). 05 WS STUDENT NAME PIC X (25). 05 WS-STUDENT-ADDRESS X (50). EXEC SQL END DECLARE SECTION END-EXEC. PROCEDURE DIVISION. MOVE 1005 TO WS-STUDENT-ID. EXEC SQL DELETE FROM STUDENT WHERE STUDENT-ID =: WS-STUDENT-ID END-EXEC. IF SQLCODE = 0 DISPLAY 'Record Deleted Successfully' ELSE DISPLAY 'Error' END-IF. STOP RUN.

JCL to execute the above COBOL program -

// SAMPLE JOB (TESTJCL, XXXXXX), CLASS = A, MSGCLASS = C // STEP001 EXEC PGM = IKJEFT01 // STEPLIB DD DSN = MYDATA.URMI.DBRMLIB, DISP = SHR // SYSPRINT DD SYSOUT = * // SYSUDUMP DD SYSOUT = * // SYSOUT DD SYSOUT = * // SYSTSIN DD * DSN SYSTEM (SSID) RUN PROGRAM (HELLO) PLAN (PLANNAME) - END / *

When you compile and execute the above program, it produces the following result -

Record Deleted Successfully

Cursors

Cursors are used to handle multiple row selections at a time. They are data structures that hold all the results of a query. They can be defined in the Working-Storage Section or the Procedure Division. Following are the operations associated with Cursor -

Declare cursor

Cursor declaration can be done in the Working-Storage Section or the Procedure Division. The first statement is the DECLARE statement which is a nonexecutable statement.

EXEC SQL DECLARE STUDCUR CURSOR FOR SELECT STUDENT-ID, STUDENT-NAME, STUDENT-ADDRESS FROM STUDENT WHERE STUDENT-ID>: WS-STUDENT-ID END-EXEC.

Open

Before using a cursor, Open statement must be performed. The open statement prepares the SELECT for execution.

EXEC SQL OPEN STUDCUR END-EXEC.

Close

Close statement releases all the memory occupied by the cursor. It is mandatory to close a cursor before ending a program.

EXEC SQL CLOSE STUDCUR END-EXEC.

Fetch

Fetch statement identifies the cursor and puts the value in the INTO clause. A fetch statement is coded in loop as we get one row at a time.

EXEC SQL FETCH STUDCUR INTO: WS-STUDENT-ID,: WS-STUDENT-NAME, WS-STUDENT-ADDRESS END-EXEC.

The following example shows the usage of cursor to fetch all the records from the STUDENT table -

IDENTIFICATION DIVISION. PROGRAM ID. HELLO. DATA DIVISION. WORKING STORAGE SECTION. EXEC SQL INCLUDE SQLCA END-EXEC. EXEC SQL INCLUDE STUDENT END-EXEC. EXEC SQL BEGIN DECLARE SECTION END-EXEC. 01 WS-STUDENT-REC. 05 WS-STUDENT-ID PIC 9 (4). 05 WS STUDENT NAME PIC X (25). 05 WS-STUDENT-ADDRESS X (50). EXEC SQL END DECLARE SECTION END-EXEC. EXEC SQL DECLARE STUDCUR CURSOR FOR SELECT STUDENT-ID, STUDENT-NAME, STUDENT-ADDRESS FROM STUDENT WHERE STUDENT-ID>: WS-STUDENT-ID END-EXEC. PROCEDURE DIVISION. MOVE 1001 TO WS-STUDENT-ID. PERFORM UNTIL SQLCODE = 100 EXEC SQL FETCH STUDCUR INTO: WS-STUDENT-ID,: WS-STUDENT-NAME, WS-STUDENT-ADDRESS END-EXEC DISPLAY WS-STUDENT-REC END-PERFORM STOP RUN.

JCL to execute the above COBOL program -

// SAMPLE JOB (TESTJCL, XXXXXX), CLASS = A, MSGCLASS = C // STEP001 EXEC PGM = IKJEFT01 // STEPLIB DD DSN = MYDATA.URMI.DBRMLIB, DISP = SHR // SYSPRINT DD SYSOUT = * // SYSUDUMP DD SYSOUT = * // SYSOUT DD SYSOUT = * // SYSTSIN DD * DSN SYSTEM (SSID) RUN PROGRAM (HELLO) PLAN (PLANNAME) - END / *

When you compile and execute the above program, it produces the following result -

1001 Mohtashim M. Hyderabad 1002 Nishant Malik Delhi 1003 Amitabh Bachan Mumbai 1004 Chulbul Pandey Lucknow