COBOL-数据库接口 - 芒果文档

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📜 COBOL-数据库接口

📅 最后修改于: 2020-11-22 16:58:27 🧑 作者: Mango

到目前为止，我们已经了解了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
游标

嵌入式SQL

嵌入式SQL语句在COBOL程序中用于执行标准SQL操作。在编译应用程序之前，嵌入式SQL语句将由SQL处理器进行预处理。 COBOL被称为宿主语言。 COBOL-DB2应用程序是那些同时包含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，但有一些小的更改。例如，查询的输出被定向到一组预定义的变量，这些变量被称为“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

以下是编码COBOL-DB2程序时要遵循的规则-

必须在EXEC SQL和ENDEXEC之间定界所有SQL语句。。
SQL语句必须在区域B中编码。
程序中使用的所有表都必须在WorkingStorage部分中声明。这是通过使用INCLUDE语句完成的。
除INCLUDE和DECLARE TABLE之外的所有SQL语句都必须出现在Procedure Division中。

主机变量

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

宿主变量不能是组项目，但可以在宿主结构中将它们分组在一起。它们不能重命名或重新定义。在SQL语句中使用主机变量，请在它们前面加上冒号(:)。 。

句法

以下是声明主机变量并在Working-Storage部分中包含表的语法-

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通过该通信区域将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中声明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“ Student”的表，其中包含Student-Id，Student-Name和Student-Address。

学生表包含以下数据-

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SELECT查询在COBOL程序中的用法-

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，它将产生以下结果-

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，它将产生以下结果-

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，它将产生以下结果-

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，它将产生以下结果-

Record Deleted Successfully

游标

游标用于一次处理多个行选择。它们是保存查询所有结果的数据结构。它们可以在“工作存储”部分或“程序”部分中定义。以下是与游标相关联的操作-

宣布
打开
关
取

声明游标

游标声明可以在“工作存储”部分或“程序”部分中进行。第一条语句是DECLARE语句，它是不可执行的语句。

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

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.

取

Fetch语句标识游标，并将值放在INTO子句中。当我们一次获取一行时，Fetch语句被循环编码。

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，它将产生以下结果-

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