嵌入式SQL

在SQL语句中,,使用主变量 和  指示变量的方法

exec sql begin declare section; 
 char id[6];
 smallint indic;
 char pub_name[41];
exec sql end declare section;

exec sql select pub_id into :id indicator :indic 
from titles 
where title like "%Stress%";
if (indic == -1)
{ printf("\npub_id is null"); } 
else
{
 exec sql select pub_name into :pub_name 
from publishers 
where pub_id = :id; 
printf("\nPublisher: %s", pub_name);
}

程序实例： 依次检查某个系的学生记录，交互式更新某些学生年龄


EXEC SQL BEGIN DEC LARE SECTION;  /*主变量说明开始*/ 
    char deptname[64];
    char HSno[64];
    char HSname[64]; 
    char HSsex[64];
    int     HSage;
    int    NEWAGE;
EXEC SQL END DECLARE SECTION;     /*主变量说明结束*/


long SQLCODE;
EXEC SQL INCLUDE sqlca;                    /*定义SQL通信区*/
int main(void)                           /*C语言主程序开始*/
{    int     count = 0;    
     char  yn;                                 /*变量yn代表yes或no*/
    printf("Please choose the department name(CS/MA/IS): "); 
    scanf("%s", deptname);                    /*为主变量deptname赋值*/
    EXEC SQL CONNECT TO TEST@localhost:54321 USER"SYSTEM" /"MANAGER";         /*连接数据库TEST*/
    EXEC SQL DECLARE SX CURSOR FOR   /*定义游标*/


        SELECT Sno, Sname, Ssex, Sage   /*SX对应语句的执行结果*/
        FROM Student
        WHERE SDept = :deptname;
    EXEC SQL OPEN SX;        /*打开游标SX便指向查询结果的第一行*/



for ( ; ; )             /*用循环结构逐条处理结果集中的记录*/
{                                      /*推进游标，将当前数据放入主变量*/
    EXEC SQL FETCH SX INTO :HSno, :HSname, :HSsex,:HSage;
     if (sqlca.sqlcode != 0)     /* sqlcode != 0,表示操作不成功*/
        break;                        /*利用SQLCA中的状态信息决定何时退出循环*/
    if(count++ == 0)             /*如果是第一行的话，先打出表头*/
         printf("\n%-10s %-20s %-10s %-10s\n", "Sno", "Sname", "Ssex", "Sage");

   /*打印查询结果*/    
     printf("%-10s %-20s %-10s %-10d\n", HSno, HSname, HSsex, HSage);  
    /*询问用户是否要更新该学生的年龄*/
     printf("UPDATE AGE(y/n)?"); 

     do{                     
          scanf("%c",&yn);
      } while(yn != ‘N‘ && yn != ‘n‘ && yn != ‘Y‘ && yn != ‘y‘);
        


if (yn == ‘y‘ || yn == ‘Y‘)                 /*如果选择更新操作*/
{         printf("INPUT NEW AGE:");
         scanf("%d",&NEWAGE);          /*用户输入新年龄到主变量中*/


         EXEC SQL UPDATE Student               /*嵌入式SQL*/
            SET Sage = :NEWAGE
            WHERE CURRENT OF SX ;
        }      /*对当前游标指向的学生年龄进行更新*/
}





     EXEC SQL CLOSE SX; /*关闭游标SX不再和查询结果对应*/
    EXEC SQL COMMIT WORK;                           /*提交更新*/
    EXEC SQL DISCONNECT TEST;        /*断开数据库连接*/
}