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PostgreSQL连接C/C++接口实例(2)

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SELECT操作符

下面的C代码段，表明我们如何能够获取并显示在上面的例子中创建COMPANY表的记录：

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#include <iostream>
#include <pqxx/pqxx> 

using namespace std;
using namespace pqxx;

int main(int argc, char* argv[])
{
   char * sql;
   
   try{
      connection C("dbname=testdb user=postgres password=cohondob \
      hostaddr=127.0.0.1 port=5432");
      if (C.is_open()) {
         cout << "Opened database successfully: " << C.dbname() << endl;
      } else {
         cout << "Can't open database" << endl;
         return 1;
      }
      /* Create SQL statement */
      sql = "SELECT * from COMPANY";

      /* Create a non-transactional object. */
      nontransaction N(C);
      
      /* Execute SQL query */
      result R( N.exec( sql ));
      
      /* List down all the records */
      for (result::const_iterator c = R.begin(); c != R.end(); ++c) {
         cout << "ID = " << c[0].as<int>() << endl;
         cout << "Name = " << c[1].as<string>() << endl;
         cout << "Age = " << c[2].as<int>() << endl;
         cout << "Address = " << c[3].as<string>() << endl;
         cout << "Salary = " << c[4].as<float>() << endl;
      }
      cout << "Operation done successfully" << endl;
      C.disconnect ();
   }catch (const std::exception &e){
      cerr << e.what() << std::endl;
      return 1;
   }

   return 0;
} 
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上述程序编译和执行时，它会产生以下结果： yiibai.com 

Opened database successfully: testdb
ID = 1
Name = Paul
Age = 32
Address = California
Salary = 20000
ID = 2
Name = Allen
Age = 25
Address = Texas
Salary = 15000
ID = 3
Name = Teddy
Age = 23
Address = Norway
Salary = 20000
ID = 4
Name = Mark
Age = 25
Address = Rich-Mond
Salary = 65000
Operation done successfully
 
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UPDATE 操作

下面的C代码段显示了我们如何使用UPDATE语句来更新任何记录，然后从COMPANY表获取并显示更新的记录：

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#include <iostream>
#include <pqxx/pqxx> 

using namespace std;
using namespace pqxx;

int main(int argc, char* argv[])
{
   char * sql;
   
   try{
      connection C("dbname=testdb user=postgres password=cohondob \
      hostaddr=127.0.0.1 port=5432");
      if (C.is_open()) {
         cout << "Opened database successfully: " << C.dbname() << endl;
      } else {
         cout << "Can't open database" << endl;
         return 1;
      }
      
      /* Create a transactional object. */
      work W(C);
      /* Create  SQL UPDATE statement */
      sql = "UPDATE COMPANY set SALARY = 25000.00 where ID=1";
      /* Execute SQL query */
      W.exec( sql );
      W.commit();
      cout << "Records updated successfully" << endl;
      
      /* Create SQL SELECT statement */
      sql = "SELECT * from COMPANY";

      /* Create a non-transactional object. */
      nontransaction N(C);
      
      /* Execute SQL query */
      result R( N.exec( sql ));
      
      /* List down all the records */
      for (result::const_iterator c = R.begin(); c != R.end(); ++c) {
         cout << "ID = " << c[0].as<int>() << endl;
         cout << "Name = " << c[1].as<string>() << endl;
         cout << "Age = " << c[2].as<int>() << endl;
         cout << "Address = " << c[3].as<string>() << endl;
         cout << "Salary = " << c[4].as<float>() << endl;
      }
      cout << "Operation done successfully" << endl;
      C.disconnect ();
   }catch (const std::exception &e){
      cerr << e.what() << std::endl;
      return 1;
   }

   return 0;
} 
www.yiibai.com

上述程序编译和执行时，它会产生以下结果：

yiibai.com

Opened database successfully: testdb
Records updated successfully
ID = 2
Name = Allen
Age = 25
Address = Texas
Salary = 15000
ID = 3
Name = Teddy
Age = 23
Address = Norway
Salary = 20000
ID = 4
Name = Mark
Age = 25
Address = Rich-Mond
Salary = 65000
ID = 1
Name = Paul
Age = 32
Address = California
Salary = 25000
Operation done successfully
 www.yiibai.com

DELETE 操作

下面的C代码段显示了我们如何使用DELETE语句删除任何记录，然后获取并显示剩余的记录COMPANY 表： 
 
#include <iostream>
#include <pqxx/pqxx> 

using namespace std;
using namespace pqxx;

int main(int argc, char* argv[])
{
   char * sql;
   
   try{
      connection C("dbname=testdb user=postgres password=cohondob \
      hostaddr=127.0.0.1 port=5432");
      if (C.is_open()) {
         cout << "Opened database successfully: " << C.dbname() << endl;
      } else {
         cout << "Can't open database" << endl;
         return 1;
      }
      
      /* Create a transactional object. */
      work W(C);
      /* Create  SQL DELETE statement */
      sql = "DELETE from COMPANY where ID = 2";
      /* Execute SQL query */
      W.exec( sql );
      W.commit();
      cout << "Records deleted successfully" << endl;
      
      /* Create SQL SELECT statement */
      sql = "SELECT * from COMPANY";

      /* Create a non-transactional object. */
      nontransaction N(C);
      
      /* Execute SQL query */
      result R( N.exec( sql ));
      
      /* List down all the records */
      for (result::const_iterator c = R.begin(); c != R.end(); ++c) {
         cout << "ID = " << c[0].as<int>() << endl;
         cout << "Name = " << c[1].as<string>() << endl;
         cout << "Age = " << c[2].as<int>() << endl;
         cout << "Address = " << c[3].as<string>() << endl;
         cout << "Salary = " << c[4].as<float>() << endl;
      }
      cout << "Operation done successfully" << endl;
      C.disconnect ();
   }catch (const std::exception &e){
      cerr << e.what() << std::endl;
      return 1;
   }

   return 0;
} 
yiibai.com

上述程序编译和执行时，它会产生以下结果：

www.yiibai.com

Opened database successfully: testdb
Records deleted successfully
ID = 3
Name = Teddy
Age = 23
Address = Norway
Salary = 20000
ID = 4
Name = Mark
Age = 25
Address = Rich-Mond
Salary = 65000
ID = 1
Name = Paul
Age = 32
Address = California
Salary = 25000
Operation done successfully 
yiibai.com
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