程序中变量和SQL中的变量或某个计算出来的值如何交互?

[yingpf]

1、通过ODBC连接数据库，我该如何得到用SQL得到的单值？如：一个age字段，我要取其最大值，我可以执行一个SQL：“select max(age) from student”,问题是我如何将这个最大值赋值给我的程序的一个变量？

现在我的做法是，用“select * from student order by age desc”打开一个recordset，然后取这个recordset第一个记录的age字段值（变量m_nAge映射到当前记录的age字段），但这样做太笨了。

2、ODBC如何执行一个SQL存储过程？如果这个存储过程有返回值的话，我又该怎么得到这个返回值呢？还有如果这个存储过程有参数的话，我又如何把我程序中的变量传过去呢？我其实就是想知道程序中变量和SQL中的变量如何交互？

[oyljerry]

1,_variant_t vIndex = (long)0;
_variant_t vCount = m_pRecordset2->GetCollect(vIndex);
vCount.lval就是你要 的值了

[zhangqu_980371]

1.select max(age) as m_age from student
按照你正常的读取记录值“m_age ”就可以了。没有问题的。

2。按你的意思上一无需要写存储过程的。例如:
sprintf(strSql,"update tablename set aa=参数...",参数...);
sprintf(strSql,"select a * 参数1，b + 参数2 ... from tablename where c = 参数3...",参数1,参数2,参数3...);
至于你查询返回的结果用上面第1点就可以。

[Kudeet]

1
select max(age) as temp from student
_variant_t var = m_pset->GetCollect("temp");
var.iVal里保存就是你要的值

2
问】CRecordset类如何访问存储过程取得返回值？
答】
用MFC ODBC
重载crecordset:
//chcode.h
class chcode : public CRecordset
{
public:
void Move( long nrows, WORD wfetchtype );
chcode(CDatabase* pDatabase = NULL);
DECLARE_DYNAMIC(chcode)

// Field/Param Data
//{{AFX_FIELD(chcode, CRecordset)
long m_retreturn_value;
CString m_newpassword;
CString m_oldpassword;
CString m_username;
//}}AFX_FIELD


// Overrides
// ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(chcode)
public:
virtual CString GetDefaultConnect(); // Default connection string
virtual CString GetDefaultSQL(); // Default SQL for Recordset
virtual void DoFieldExchange(CFieldExchange* pFX); // RFX support
//}}AFX_VIRTUAL

// Implementation
#ifdef _DEBUG
virtual void AssertValid() const;
virtual void Dump(CDumpContext& dc) const;
#endif
};

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

#endif // !defined(AFX_CHCODE_H__FF9F8501_31F2_4794_B697_B7FFB5A15C30__INCLUDED_)
//chcode.cpp
// chcode.cpp : implementation file
//

#include "stdafx.h"
#include "chcode.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////////
// chcode
void AFXAPI RFX_Textout(CFieldExchange * pfx, LPCTSTR szname,
CString& value, int nmaxlength, int ncolumntype, short nscale);
IMPLEMENT_DYNAMIC(chcode, CRecordset)

chcode::chcode(CDatabase* pdb)
: CRecordset(pdb)
{
//{{AFX_FIELD_INIT(chcode)
m_oldpassword="";
m_newpassword="";
m_username="";
//}}AFX_FIELD_INIT
m_nDefaultType = snapshot;
m_nParams=4; }


CString chcode::GetDefaultConnect()
{
return _T("ODBC;DSN=");
}

CString chcode::GetDefaultSQL()
{
return _T("");
}

void chcode::DoFieldExchange(CFieldExchange* pFX)
{
//{{AFX_FIELD_MAP(chcode)
pFX->SetFieldType(CFieldExchange ::outputParam); //set the field type to outputParam for the return value
RFX_Long(pFX, _T("return_value"), m_retreturn_value); //bind the return value to the variable
pFX->SetFieldType(CFieldExchange ::inputParam); //reset the field type to inputParam
RFX_Text(pFX, "@old", m_oldpassword);//,255,SQL_CHAR,0);
RFX_Text(pFX, "@new", m_newpassword);//,255,SQL_CHAR,0); //call the new rfx_Text to get the character output params
RFX_Text(pFX, "@loginame", m_username);//,255,SQL_CHAR,0);
//}}AFX_FIELD_MAP
}

/////////////////////////////////////////////////////////////////////////////
// chcode diagnostics

#ifdef _DEBUG
void chcode::AssertValid() const
{
CRecordset::AssertValid();
}

void chcode::Dump(CDumpContext& dc) const
{
CRecordset::Dump(dc);
}
#endif //_DEBUG
//Move(long nRows, WORD wFetchType)
void chcode::Move(long nrows, WORD wfetchtype)
{
if (m_nFields)
CRecordset ::Move(nrows, wfetchtype);
else
m_bBOF = m_bEOF = true;
}


调用:

CDatabase db1;
s1.Format("ODBC;UID=sa;PWD=%s","");
db1.Open("report",false,false,s1);
chcode chrs(&db1);
//CRecordset rs(&db1);
chrs.m_newpassword=in.m1;
chrs.m_oldpassword=s3;
chrs.m_username="report";
chrs.Open( AFX_DB_USE_DEFAULT_TYPE ,_T("{?=CALL sp_password(?,?,?)}"));
//chrs.Open(AFX_DB_USE_DEFAULT_TYPE,"{call sp_password('report','report','report')}");
//chrs.m_retreturn_value;这就是返回值
chrs.Close();
db1.Close();

你也可以去看看下面的例子：
http://www.codeproject.com/database/mssqltutorial.asp
http://www.codeproject.com/database/MyRecordset.asp
http://www.codeproject.com/database/spcw.asp

[llm06]

老大，用个别名就可以了，直接访问别名

[chinaseven]

CRecordset rs(&g_MJDatabase);
strSQL.Format("select employeeid as EMPLOYEE ,cardtypeid as CARDTYPE,cardstatusid as CARDSTATUS from ccard where factoryfixid=%ld",lSerID);
try
{
rs.Open(CRecordset::forwardOnly,strSQL);
if(!rs.IsEOF())
{
rs.GetFieldValue("EMPLOYEE",strEmp);
rs.GetFieldValue("CARDTYPE",strType);
rs.GetFieldValue("CARDSTATUS",strStatus);
rs.Close();
}

[yingpf]

老大，下面的写法会引起异常：“无效的描述符索引 ”
CString strName;
CDatabase db;
CString strConnect = _T("DRIVER=SQL SERVER; SERVER=127.0.0.1; UID=sa; PWD=123456; DATABASE=student");
CString strSQL = _T("select * from s");

db.OpenEx(strConnect, CDatabase::noOdbcDialog);

CStu rSet(&db);
rSet.Open(CRecordset::forwardOnly, strSQL);
rSet.GetFieldValue("sname", strName); //这句引发异常，sname是一个字段:sname char(8)

[yingpf]

??

[yingpf]

大爷们，帮忙啊