目录
  1. WIKI教程
  2. 学习COBOL
  3. COBOL - 数据库接口( Database Interface)

COBOL - 数据库接口( Database Interface)

截至目前，我们已经学会了在COBOL中使用文件。 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应用程序编程
  • 主机变量
  • SQLCA
  • SQL查询
  • 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。 在编译应用程序之前，SQL处理器会对嵌入式SQL语句进行预处理。 COBOL被称为Host Language 。 COBOL-DB2应用程序是包含COBOL和DB2的应用程序。

嵌入式SQL语句的工作方式与普通的SQL语 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 。 另一个INTO子句放在SELECT语句中。

DB2应用程序编程

以下是编写COBOL-DB2程序时要遵循的规则 -

  • 必须在EXEC SQL和ENDEXEC.之间分隔所有SQL语句ENDEXEC. 。

  • SQL语句必须在区域B中编码。

  • 必须在WorkingStorage部分声明程序中使用的所有表。 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。 它们在工作储存科申报。

主变量不能是组项，但它们可以在主机结构中组合在一起。 它们无法Renamed或Redefined 。 将主变量与SQL语句一起使用，用colon (:).作为前缀colon (:). 。

语法 (Syntax)

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通过该区域将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，如SQLCODE ，它包含错误代码。 SQLCODE中的值'000'表示成功执行。

语法 (Syntax)

以下是在Working-Storage部分声明SQLCA的语法 - 

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

SQL Queries

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

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
/*

编译并执行上述程序时，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 'IoWiki' 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
/*

编译并执行上述程序时，会产生以下结果 - 

Record Inserted Successfully
1005 IoWiki		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
/*

编译并执行上述程序时，会产生以下结果 - 

Record Updated Successfully

以下example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
/*

编译并执行上述程序时，会产生以下结果 - 

Record Deleted Successfully

Cursors

游标用于一次处理多行选择。 它们是包含查询所有结果的数据结构。 它们可以在工作 - 存储部分或程序部门中定义。 以下是与光标相关的操作 -

  • Declare
  • Open
  • Close
  • Fetch

声明游标

游标声明可以在工作存储部分或程序部门完成。 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执行。 

EXEC SQL
   OPEN STUDCUR
END-EXEC.

Close

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光标。 

EXEC SQL
   CLOSE STUDCUR
END-EXEC.

Fetch

Fetch语句标识游标并将值放入INTO子句中。 Fetch语句在循环中编码，因为我们一次获得一行。 

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

以下示例显示了游标用于从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
/*

编译并执行上述程序时，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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