• COBOL 视频教程

COBOL - 数据库接口

到目前为止，我们已经学会了COBOL中文件的使用。现在，我们将讨论 COBOL 程序如何与 DB2 交互。它涉及以下术语 -

  • 嵌入式SQL
  • DB2 应用程序编程
  • 主机变量
  • SQLCA
  • SQL查询
  • 光标

嵌入式SQL

COBOL 程序中使用嵌入式 SQL 语句来执行标准 SQL 操作。嵌入式 SQL 语句在应用程序编译之前由 SQL 处理器进行预处理。COBOL 被称为宿主语言。COBOL-DB2 应用程序是指同时包含 COBOL 和 DB2 的应用程序。

嵌入式 SQL 语句的工作方式与普通 SQL 语句类似，但有一些细微的变化。例如，查询的输出定向到一组预定义的变量，这些变量称为“主机变量”。SELECT 语句中放置了一个附加的 INTO 子句。

DB2 应用程序编程

以下是编写 COBOL-DB2 程序时应遵循的规则 -

  • 所有 SQL 语句都必须在EXEC SQL和ENDEXEC之间分隔。。

  • SQL语句必须在B区编码。

  • 程序中使用的所有表都必须在工作存储部分中声明。这是通过使用INCLUDE语句来完成的。

  • 除 INCLUDE 和 DECLARE TABLE 之外的所有 SQL 语句都必须出现在过程分区中。

主机变量

主机变量用于从表接收数据或向表插入数据。必须为要在程序和 DB2 之间传递的所有值声明主变量。它们在工作存储部分中声明。

主变量不能是组项，但它们可以在主结构中分组在一起。它们不能被重命名或重新定义。将主变量与 SQL 语句一起使用，请在它们前面加上冒号 (:)。。

句法

以下是声明主机变量并在工作存储部分包含表的语法 -

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 是一个 SQL 通信区域，DB2 通过它将 SQL 执行的反馈传递给程序。它告诉程序执行是否成功。SQLCA 下有许多预定义变量，例如包含错误代码的SQLCODE 。SQLCODE 中的值“000”表示执行成功。

句法

以下是在工作存储部分声明 SQLCA 的语法 -

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

SQL查询

假设我们有一个名为“学生”的表，其中包含学生 ID、学生姓名和学生地址。

STUDENT 表包含以下数据 -

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

以下示例显示了COBOL 程序中SELECT查询的用法-

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执行上述 COBOL 程序 -

//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
/*

当您编译并执行上述程序时，它会产生以下结果 -

1004 Chulbul Pandey		Lucknow

以下示例显示了COBOL 程序中INSERT查询的用法-

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执行上述 COBOL 程序 -

//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
/*

当您编译并执行上述程序时，它会产生以下结果 -

Record Inserted Successfully
1005 TutorialsPoint		Hyderabad

以下示例显示了COBOL 程序中UPDATE查询的用法-

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执行上述 COBOL 程序 -

//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
/*

当您编译并执行上述程序时，它会产生以下结果 -

Record Updated Successfully

以下示例显示了COBOL 程序中DELETE查询的用法-

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执行上述 COBOL 程序 -

//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
/*

当您编译并执行上述程序时，它会产生以下结果 -

Record Deleted Successfully

光标

游标用于一次处理多个行选择。它们是保存所有查询结果的数据结构。它们可以在工作存储部分或程序部分中定义。以下是与光标相关的操作 -

  • 宣布
  • 打开
  • 关闭
  • 拿来

声明游标

游标声明可以在工作存储部分或过程部分中完成。第一条语句是 DECLARE 语句，它是一个不可执行的语句。

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

打开

在使用游标之前，必须执行Open 语句。Open 语句准备执行 SELECT。

EXEC SQL
   OPEN STUDCUR
END-EXEC.

关闭

Close语句释放游标占用的所有内存。在结束程序之前必须关闭游标。

EXEC SQL
   CLOSE STUDCUR
END-EXEC.

拿来

Fetch 语句标识游标并将值放入 INTO 子句中。Fetch 语句是在循环中编码的，因为我们一次获取一行。

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

以下示例显示了如何使用游标从 STUDENT 表中获取所有记录 -

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执行上述 COBOL 程序 -

//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
/*

当您编译并执行上述程序时，它会产生以下结果 -

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