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  COBOL - 数据库接口

  • 简述

    至此，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。它涉及以下条款 -
    • 嵌入式 SQL
    • DB2 应用程序
    • 宿主变量
    • SQLCA
    • SQL Queries
    • Cursors

  • 嵌入式 SQL

    嵌入式 SQL 语句在 COBOL 程序中用于执行标准 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Host Language. 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，但有一些细微的变化。例如，查询的输出指向一组预定义的变量，这些变量称为Host Variables. 在 SELECT 语句中放置了一个额外的 INTO 子句。

  • DB2 应用程序编程

    以下是编写 COBOL-DB2 程序时要遵循的规则 -
    • 所有 SQL 语句必须在EXEC SQL和ENDEXEC..
    • 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陈述。
    • 除 INCLUDE 和 DECLARE TABLE 之外的所有 SQL 语句都必须出现在 Procedure Division 中。

  • 宿主变量

    宿主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变量。它们在工作存储部分中声明。
    宿主变量不能是组项，但它们可以在宿主结构中组合在一起。他们不能Renamed或者Redefined. 在 SQL 语句中使用主机变量，在它们前面加上前缀colon (:)..

    句法

    以下是声明主机变量并在工作存储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 下有许多预定义的变量，例如SQLCODE其中包含错误代码。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。
    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
    下面的例子展示了SELECT在 COBOL 程序中查询 - 
    
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
    下面的例子展示了INSERT在 COBOL 程序中查询 - 
    
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
    下面的例子展示了UPDATE在 COBOL 程序中查询 - 
    
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example显示的用法DELETE在 COBOL 程序中查询 - 
    
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
    • 拿来

    声明光标

    光标声明可以在工作存储部分或程序部分完成。第一个语句是 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.

    OPEN

    在使用游标之前，必须执行 Open 语句。Open 语句准备 SELECT 以供执行。 
    
EXEC SQL
   OPEN STUDCUR
END-EXEC.

    关

    关闭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.

    Fetch

    Fetch 语句识别游标并将值放在 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.
    以下示例显示了使用游标从 STUDENT 表中获取所有记录的用法 - 
    
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.
   
   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
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