“G”术时刻：Linux环境下通过ESQL/C方式连接南大通用GBase 8s数据库（下）

在 Linux 环境中，使用 C 语言通过 ESQL/C 方式连接南大通用 GBase 8s 数据库是常见的开发需求。ESQL/C 是一种允许在 C 程序中嵌入 SQL 语句的技术。通过 ESQL/C，开发者可以在 C 程序中直接操作数据库，实现数据的增删改查等功能。本文将通过一个完整的示例，详细介绍如何在 Linux 下通过 ESQL/C 连接 GBase 8s 数据库，包括环境搭建、代码编写、编译和运行等步骤。

ESQL/C 代码示例

以下是一个完整的 ESQL/C 示例代码，展示如何连接到 GBase 8s 数据库并执行一些基本操作。

示例代码

#include <stdio.h>
EXEC SQL define NAME_LEN 20;
EXEC SQL define ADDRESS_LEN 200;
main()
{
   EXEC SQL BEGIN DECLARE SECTION;
   int rnum;
   int snum;
   char sname[NAME_LEN + 1];
   char saddress[ADDRESS_LEN + 1];
   EXEC SQL END DECLARE SECTION;
   EXEC SQL WHENEVER ERROR STOP;
   EXEC SQL connect to 'testzh';
   // Drop table
   EXEC SQL drop table if exists tab2;
   printf("Drop table successfully.\n\n");
   // Create table
   EXEC SQL create table tab2 (num int, name char(20), address varchar2(200));
   printf("Create table successfully.\n\n");
   // Insert without using host variables
   EXEC SQL insert into tab2 values (1, "Jack", "Beijing");
   printf("Insert (without using host variables) successfully.\n\n");
   // Insert using host variables
   snum = 2;
   sprintf(sname, "Mary");
   sprintf(saddress, "Shanghai");
   EXEC SQL insert into tab2 values (:snum, :sname, :saddress);
   printf("Insert (with using host variables) successfully.\n\n");
   // Use a static SQL statement to select data
   EXEC SQL declare mycursor1 cursor for
   select num, name, address from tab2;
   EXEC SQL open mycursor1;
   printf("The output of the first select statement:\n");
   for (;;)
   {
       EXEC SQL fetch mycursor1 into :snum, :sname, :saddress;
       if (strncmp(SQLSTATE, "00", 2) != 0)
           break;
       printf("%d %s %s\n", snum, sname, saddress);
   }
   if (strncmp(SQLSTATE, "02", 2) != 0)
       printf("SQLSTATE after fetch is %s\n", SQLSTATE);
   EXEC SQL close mycursor1;
   EXEC SQL free mycursor1;
   // Use a dynamic SQL statement to select data
   EXEC SQL prepare mystmt from "select num, name, address from tab2 where num = ?";
   EXEC SQL declare mycursor2 cursor for mystmt;
   rnum = 2;
   EXEC SQL open mycursor2 using :rnum;
   printf("\nThe output of the second select statement:\n");
   for (;;)
   {
       EXEC SQL fetch mycursor2 into :snum, :sname, :saddress;
       if (strncmp(SQLSTATE, "00", 2) != 0)
           break;
       printf("%d %s %s\n", snum, sname, saddress);
   }
   if (strncmp(SQLSTATE, "02", 2) != 0)
       printf("SQLSTATE after fetch is %s\n", SQLSTATE);
   EXEC SQL close mycursor2;
   EXEC SQL free mystmt;
   EXEC SQL free mycursor2;
   EXEC SQL disconnect current;
   exit(0);
}

编译和运行

1、将代码保存为Demo.ec文件。

2、使用esql命令编译：

  esql Demo.ec

3、编译生成的 C 文件：

  gcc -o Demo Demo.c -I${GBASEDBTDIR}/include -L${GBASEDBTDIR}/lib -lcli

4、运行程序：

  ./Demo

程序运行结果

运行上述程序后，你将看到以下输出：

Drop table successfully.
Create table successfully.
Insert (without using host variables) successfully.
Insert (with using host variables) successfully.
The output of the first select statement:
1 Jack Beijing
2 Mary Shanghai
The output of the second select statement:
2 Mary Shanghai

  通过本文的介绍，相信您已经了解了如何在 Linux 下通过 ESQL/C 连接 GBase 8s 数据了。