aotu modify table ' field's value,by ODBC directly is false,but use CDatabase can well and also the header file is needed.

//1:

header:
// stdafx.h : include file for standard system include files,
//  or project specific include files that are used frequently, but
//      are changed infrequently
//

#if !defined(AFX_STDAFX_H__A991CDF0_663C_4755_AC58_14C3A8EF4FE0__INCLUDED_)
#define AFX_STDAFX_H__A991CDF0_663C_4755_AC58_14C3A8EF4FE0__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

#define VC_EXTRALEAN  // Exclude rarely-used stuff from Windows headers

#include <afxwin.h>         // MFC core and standard components
#include <afxext.h>         // MFC extensions
#include <afxdisp.h>        // MFC Automation classes

#ifndef _AFX_NO_DB_SUPPORT
#include <afxdb.h>   // MFC ODBC database classes
#endif // _AFX_NO_DB_SUPPORT

#ifndef _AFX_NO_DAO_SUPPORT
#include <afxdao.h>   // MFC DAO database classes
#endif // _AFX_NO_DAO_SUPPORT

#include <afxdtctl.h>  // MFC support for Internet Explorer 4 Common Controls
#ifndef _AFX_NO_AFXCMN_SUPPORT
#include <afxcmn.h>   // MFC support for Windows Common Controls
#endif // _AFX_NO_AFXCMN_SUPPORT

//{{AFX_INSERT_LOCATION}}
// Microsoft Visual C++ will insert additional declarations immediately before the previous line.

#endi

2:teset odbc.
void CTESTDBSQLDlg::OnBUTTONTESTdb()
{
 //here try use odbc directly to get objid.
 //#include <SQL.H>
 //#include <SQLEXT.H>
 //ODBC32.LIBneed!!!!!!!1
  RETCODE rcode;

  HENV henv1;
  HDBC hdbc1;
  HSTMT hstmt1;

 //char szFirstName[50];
 char szLastName[50];
 char field1[50];
 char field2[50];
 char field3[50];
 unsigned char sql1[200]="update test2 set id1='345' where id1='3'";
 //char szPhoneNum[20];
   SDWORD sdODataLength;
    unsigned char conStringOut[256];
    //1:
    rcode = ::SQLAllocEnv(&henv1);
    if (rcode != SQL_SUCCESS) {
  AfxMessageBox("allocEnvError.");
     return;
 }
    if (rcode == SQL_SUCCESS)
    { //2:
      rcode = ::SQLAllocConnect(henv1, & hdbc1);
      if (rcode != SQL_SUCCESS) {
  AfxMessageBox("AllocConnectError.");
     return;
   }
   if (rcode == SQL_SUCCESS)
      {   //3:
          rcode = ::SQLDriverConnect(hdbc1, 0,
          (unsigned char *)"DSN=JiSheng",
          SQL_NTS, conStringOut, 256, NULL,
          SQL_DRIVER_NOPROMPT);
    if (rcode != SQL_SUCCESS) {
    AfxMessageBox("DroverCpmmectEror.");
       return;
    }
         if (rcode == SQL_SUCCESS)
   {//4:
          rcode = ::SQLAllocStmt(hdbc1, &hstmt1);
    if (rcode != SQL_SUCCESS) {
       AfxMessageBox("SQLAllocStmtEror.");
       return;
    }
          if (rcode == SQL_SUCCESS)
    {   //5:execute!
              rcode = ::SQLExecDirect(hstmt1,
             (unsigned char *)
    //"update test2 set id1='34' where id1='3'",
             "SELECT * FROM test2",
              SQL_NTS);
      if(rcode!=SQL_SUCCESS){
     AfxMessageBox("exe error.");
     }

             //6:get result by return code.
            for (rcode = ::SQLFetch(hstmt1); rcode == SQL_SUCCESS;rcode = SQLFetch(hstmt1))
            {//here we test get one and exeute one.
                //get field1:
    ::SQLGetData(hstmt1, 1, SQL_C_CHAR,
                field1, 50,  & sdODataLength);
                //get field2:
    ::SQLGetData(hstmt1,2,SQL_C_CHAR,field2,50,&sdODataLength);
    //char sql[200]="no";
    //char field[100];
    //strcat(field," and ");
    //strcat(field,field2);
    
    char fieldcom[50]="\0";
    
    strcat(fieldcom,field1);
    strcat(fieldcom,field2);
    
    char sql[200]="\0";
    strcat(sql,"update test2 set sql='");
    strcat(sql,"'fieldcom'");
                strcat(sql,"' ");
    strcat(sql," where id1='");
    strcat(sql,field1);
    strcat(sql,"'\0");
    
    //now exe update the selected one.
                //-
     rcode = ::SQLExecDirect(hstmt1,
                (unsigned char *)
    //"update test2 set sql='345' where id1='3'",
       sql,//sql,//"update test2 set id1='"+fieldcom+"' where id1='"+field1+"'",
                SQL_NTS);
     if(rcode!=SQL_SUCCESS){
     AfxMessageBox("exe error.");
     }
    //==
    
    ::MessageBox(NULL,sql,
                " from AddressBookDb ", MB_OK);
            }
            ::SQLFreeStmt(hstmt1, SQL_DROP);
          }
          ::SQLDisconnect(hdbc1);
        }
        ::SQLFreeConnect(hdbc1);
      }
      ::SQLFreeEnv(henv1);
    }

}

3:CDatabase:

void CTESTDBSQLDlg::OnTestDb2()
{
    CDatabase db;
 try{
   CString strConn;
  strConn.Format("ODBC;DSN=JiSheng;UID=;PWD=");
  if(!db.Open(NULL,FALSE,FALSE,strConn,TRUE))
  MessageBox("can not open db","info",MB_OK);
  Test1Set set;
  CString sql="select * from test2";
  set.Open(AFX_DB_USE_DEFAULT_TYPE,sql);
 
  CString insertSql;
  CString f1;
  CString f2;
  CString com;
  while(!set.IsEOF()){
  f1=set.m_id1;
  f2=set.m_id2;
  com=f1+f2;
  insertSql="update test2 set id1='"+com+"' where id1='"+f1+"'";
  AfxMessageBox(insertSql);
  db.ExecuteSQL(insertSql);
  set.MoveNext();
  }
  //db.ExecuteSQL("");
  db.Close();
 
 }catch(CDBException e){
  e.ReportError();
 }

}