第八章数据库编程

8.1 嵌入式SQL（C语言版）

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被嵌入的语言（java ,C++)等被称为宿主语言，简称主语言

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当主语言为 C 语言的时候

语法格式为
```
EXEC SQL <SQL语句>
```
当主语言为java的时候

格式为
```
#SQL {<SQL语句>}
```

以下讲解是C语言

数据库的连接和断开

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SQL执行的提交与撤销

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示例

#include <stdio.h>
#include “prompt.h”
exec sql include sqlca;
char cid_prompt[ ] = “Please enter customer id: ”;
int main()
{ exec sql begin declare section;
char cust_id[5], cust_name[14];
float cust_discnt;
char user_name[20],user_pwd[20];
exec sql end declare section;
exec sql whenever sqlerror goto report_error;
exec sql whenever not found goto notfound;
strcpy(user_name, “poneilsql”);
strcpy(user_pwd, “XXXX”);
exec sql connect :user_name identified
by :user_pwd;
while((prompt(cid_prompt,1,cust_id,4)) >=0) {
exec sql select cname,discnt
into :cust_name, :cust_discnt
from customers where cid=:cust_id;
exec sql commit work;
printf(“Customer’s name is %s and discount 
is %5.1f\n”,cust_name,cust_discnt);
continue; 
notfound: printf(“Can’t find customer %s, 
continuing\n”,cust_id); }
exec sql commit release;
return 0;
report_error:
print_dberror();
exec sql rollback release;
return 1;
}

游标

检索单行结果，可将结果直接传送到宿主程序的变量中

EXEC SQL SELECT [ALL | DISTINCT] expression [, expression…]
INTO host-variable , [host-variable, …]
FROM tableref [corr_name] [ , tableref [corr_name] …]
WHERE search_condition;

example

exec sql select Sname, Sage into :vSname, :vSage from Student where
Sname = :specName ;

检索多行结果，则需使用游标(Cursor)
- 游标是指向某检索记录集的指针
- 通过这个指针的移动，每次读一行，处理一行，再读一行… , 直至处理完毕

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#define TRUE 1
#include <stdio.h>
#include “prompt.h”
exec sql include sqlca;
exec sql begin declare section;
char cust_id[5], agent_id[14];
double dollar_sum;
exec sql end declare section;
int main()
{ char cid_prompt[ ]=“Please enter customer ID:”;
exec sql declare agent_dollars cursor for select aid,sum(dollars)
from orders where cid = :cust_id group by aid;
exec sql whenever sqlerror goto report_error;
exec sql connect to testdb;
exec sql whenever not found goto finish;
 while((prompt(cid_prompt,1,cust_id,4)) >=0) {
exec sql open agent_dollars;
while(TRUE) {
exec sql fetch agent_dollars into :agent_id, :dollar_sum;
printf(“%s %11.2f\n”,agent_id, dollar_sum);
}
finish: exec sql close agent_dollars;
exec sql commit work; 
}
exec sql disconnect current;
return 0;
report_error:
print_dberror();
exec sql rollback;
exec sql disconnect current;
return 1;
}