Recuperare righe da un set di risultati (provider OLE DB di Native Client)

Si applica a:SQL ServerDatabase SQL diAzure Istanzagestita di SQL di Azure Azure Synapse Analytics PlatformSystem (PDW)

In questo esempio viene illustrato come recuperare righe da un set di risultati. Questo esempio non è supportato in IA64.

Questo articolo richiede il AdventureWorks2022 database di esempio, che è possibile scaricare dalla home page degli esempi di Microsoft SQL Server e dei progetti della community.

Importante

Se possibile, usare l'autenticazione di Windows. Se non è disponibile, agli utenti verrà richiesto di immettere le credenziali in fase di esecuzione. Evitare di archiviare le credenziali in un file. Se è necessario rendere persistenti le credenziali, è consigliabile crittografarle usando l'API di crittografia Win32.

Esempio

Descrizione

Compilare il listato di codice C++ seguente con ole32.lib oleaut32.lib ed eseguirlo. In questa applicazione viene eseguita la connessione all'istanza predefinita di SQL Server nel computer in uso. In alcuni sistemi operativi Windows sarà necessario modificare (local) o (localhost) impostando il valore sul nome dell'istanza di SQL Server. Per connettersi a un'istanza denominata, modificare la stringa di connessione da L"(local)" a L"(local)\\nome", dove nome è l'istanza denominata. Per impostazione predefinita, SQL Server Express viene installato in un'istanza denominata. Verificare che nella variabile di ambiente INCLUDE sia presente la directory che contiene sqlncli.h.

Codice

// compile with: ole32.lib oleaut32.lib  
int InitializeAndEstablishConnection();  
int ProcessResultSet();  
  
#define UNICODE  
#define _UNICODE  
#define DBINITCONSTANTS  
#define INITGUID  
#define OLEDBVER 0x0250   // to include correct interfaces  
  
#include <stdio.h>  
#include <tchar.h>  
#include <stddef.h>  
#include <windows.h>  
#include <iostream>  
#include <oledb.h>  
#include <sqlncli.h>  
#include <msdadc.h>   // for IDataConvert  
#include <msdaguid.h>   // for IDataConvert  
  
using namespace std;  
  
IDBInitialize* pIDBInitialize = NULL;  
IDBProperties* pIDBProperties = NULL;  
IDBCreateSession* pIDBCreateSession = NULL;  
IDBCreateCommand* pIDBCreateCommand = NULL;  
ICommandText* pICommandText = NULL;  
IRowset* pIRowset = NULL;  
IColumnsInfo* pIColumnsInfo = NULL;  
  
DBCOLUMNINFO* pDBColumnInfo = NULL;  
IAccessor* pIAccessor =  NULL;  
DBPROP InitProperties[4];  
DBPROPSET rgInitPropSet[1];  
  
ULONG i, j;  
HRESULT hr;  
DBROWCOUNT cNumRows = 0;  
DBORDINAL lNumCols;  
WCHAR* pStringsBuffer;  
DBBINDING* pBindings;  
DBLENGTH ConsumerBufColOffset = 0;  
HACCESSOR hAccessor;  
DBCOUNTITEM lNumRowsRetrieved;  
HROW hRows[10];  
HROW* pRows = &hRows[0];  
  
int main() {  
   // The command to execute.  
   WCHAR* wCmdString = OLESTR("SELECT StandardCost, ListPrice FROM Production.Product WHERE ListPrice > 14.00");  
  
   // Call a function to initialize and establish connection.   
   if (InitializeAndEstablishConnection() == -1) {  
      // Handle error.  
      cout << "Failed to initialize and connect to the server.\n";  
      return -1;  
   }  
  
   // Create a session object.  
   if (FAILED(pIDBInitialize->QueryInterface( IID_IDBCreateSession,  
      (void**) &pIDBCreateSession))) {  
         cout << "Failed to obtain IDBCreateSession interface.\n";  
         // Handle error.  
         return -1;  
   }  
  
   if (FAILED(pIDBCreateSession->CreateSession( NULL,   
      IID_IDBCreateCommand,   
      (IUnknown**) &pIDBCreateCommand))) {  
         cout << "pIDBCreateSession->CreateSession failed.\n";  
         // Handle error.  
         return -1;  
   }  
  
   // Access the ICommandText interface.  
   if (FAILED(pIDBCreateCommand->CreateCommand( NULL,   
      IID_ICommandText,   
      (IUnknown**) &pICommandText))) {  
         cout << "Failed to access ICommand interface.\n";  
         // Handle error.  
         return -1;  
   }  
  
   // Use SetCommandText() to specify the command text.  
   if (FAILED(pICommandText->SetCommandText(DBGUID_DBSQL, wCmdString))) {  
      cout << "Failed to set command text.\n";  
      // Handle error.  
      return -1;  
   }  
  
   // Execute the command.  
   if (FAILED(hr = pICommandText->Execute( NULL,   
      IID_IRowset,   
      NULL,   
      &cNumRows,   
      (IUnknown **) &pIRowset))) {  
         cout << "Failed to execute command.\n";  
         // Handle error.  
         return -1;  
   }  
  
   // Process the result set.  
   ProcessResultSet();   
  
   pIRowset->Release();  
  
   // Free up memory.  
   pICommandText->Release();  
   pIDBCreateCommand->Release();  
   pIDBCreateSession->Release();  
  
   if (FAILED(pIDBInitialize->Uninitialize())) {  
      // Uninitialize is not required, but it fails if an interface  
      // has not been released.  This can be used for debugging.  
      cout << "Problem uninitializing.\n";  
   }  
  
   pIDBInitialize->Release();  
   CoUninitialize();  
};  
  
int InitializeAndEstablishConnection() {      
   CoInitialize(NULL);  
  
   // Obtain access to the SQLNCLI provider.  
   hr = CoCreateInstance( CLSID_SQLNCLI11,  
      NULL,  
      CLSCTX_INPROC_SERVER,  
      IID_IDBInitialize,  
      (void **) &pIDBInitialize);  
  
   if (FAILED(hr)) {  
      printf("Failed to get IDBInitialize interface.\n");  
      // Handle errors here.  
      return -1;  
   }  
  
   // Initialize the property values needed to establish the connection.  
   for ( i = 0 ; i < 4 ; i++ )  
      VariantInit(&InitProperties[i].vValue);  
  
   // Server name.  
   InitProperties[0].dwPropertyID = DBPROP_INIT_DATASOURCE;  
   InitProperties[0].vValue.vt = VT_BSTR;  
  
   InitProperties[0].vValue.bstrVal= SysAllocString(L"(local)");  
   InitProperties[0].dwOptions = DBPROPOPTIONS_REQUIRED;  
   InitProperties[0].colid = DB_NULLID;  
  
   // Database.  
   InitProperties[1].dwPropertyID = DBPROP_INIT_CATALOG;  
   InitProperties[1].vValue.vt = VT_BSTR;  
   InitProperties[1].vValue.bstrVal = SysAllocString(L"AdventureWorks");  
   InitProperties[1].dwOptions = DBPROPOPTIONS_REQUIRED;  
   InitProperties[1].colid = DB_NULLID;  
  
   InitProperties[2].dwPropertyID = DBPROP_AUTH_INTEGRATED;  
   InitProperties[2].vValue.vt = VT_BSTR;  
   InitProperties[2].vValue.bstrVal = SysAllocString(L"SSPI");  
   InitProperties[2].dwOptions = DBPROPOPTIONS_REQUIRED;  
   InitProperties[2].colid = DB_NULLID;  
  
   // Properties are set, now construct the DBPROPSET structure (rgInitPropSet) used to pass   
   // an array of DBPROP structures (InitProperties) to the SetProperties method.  
   rgInitPropSet[0].guidPropertySet = DBPROPSET_DBINIT;  
   rgInitPropSet[0].cProperties = 4;  
   rgInitPropSet[0].rgProperties = InitProperties;  
  
   // Set initialization properties.  
   hr = pIDBInitialize->QueryInterface(IID_IDBProperties, (void **)&pIDBProperties);  
   if (FAILED(hr)) {  
      cout << "Failed to get IDBProperties interface.\n";  
      // Handle errors here.  
      return -1;  
   }  
  
   hr = pIDBProperties->SetProperties(1, rgInitPropSet);   
   if (FAILED(hr)) {  
      cout << "Failed to set initialization properties.\n";  
      // Handle errors here.  
      return -1;  
   }  
  
   pIDBProperties->Release();  
  
   // Now establish the connection to the data source.  
   if (FAILED(pIDBInitialize->Initialize())) {  
      cout << "Problem in establishing connection to the data"  
         "source.\n";  
      // Handle errors here.  
      return -1;  
   }  
   return 0;  
}  
  
// Retrieve and display data resulting from a query.  
int ProcessResultSet() {  
   // Obtain access to the IColumnInfo interface, from the Rowset object.  
   hr = pIRowset->QueryInterface(IID_IColumnsInfo, (void **)&pIColumnsInfo);  
   if (FAILED(hr)) {  
      cout << "Failed to get IColumnsInfo interface.\n";  
      // Handle errors here.  
      return -1;  
   }   
  
   // Retrieve the column information.  
   pIColumnsInfo->GetColumnInfo(&lNumCols, &pDBColumnInfo, &pStringsBuffer);  
  
   // Free the column information interface.  
   pIColumnsInfo->Release();  
  
   // Create a DBBINDING array.  
   DBBINDING * p = (pBindings = new DBBINDING[lNumCols]);  
   if (!(p /* pBindings = new DBBINDING[lNumCols] */ ))  
      return -1;  
  
   // Using the ColumnInfo structure, fill out the pBindings array.  
   for ( j = 0 ; j < lNumCols ; j++ ) {  
      pBindings[j].iOrdinal = j+1;  
      pBindings[j].obValue = ConsumerBufColOffset;  
      pBindings[j].pTypeInfo = NULL;  
      pBindings[j].pObject = NULL;  
      pBindings[j].pBindExt = NULL;  
      pBindings[j].dwPart = DBPART_VALUE;  
      pBindings[j].dwMemOwner = DBMEMOWNER_CLIENTOWNED;  
      pBindings[j].eParamIO = DBPARAMIO_NOTPARAM;  
      pBindings[j].cbMaxLen = (pDBColumnInfo[j].wType == DBTYPE_WSTR) ? pDBColumnInfo[j].ulColumnSize * 2 : pDBColumnInfo[j].ulColumnSize;  
      pBindings[j].dwFlags = 0;  
      pBindings[j].wType = pDBColumnInfo[j].wType;  
      pBindings[j].bPrecision = pDBColumnInfo[j].bPrecision;  
      pBindings[j].bScale = pDBColumnInfo[j].bScale;  
  
      // Compute the next buffer offset.  
      ConsumerBufColOffset =   
         ConsumerBufColOffset + pBindings[j].cbMaxLen;  
   };  
  
   // Get the IAccessor interface.  
   hr = pIRowset->QueryInterface(IID_IAccessor, (void **) &pIAccessor);  
   if (FAILED(hr)) {  
      cout << "Failed to obtain IAccessor interface.\n";  
      // Handle errors here.  
      return -1;  
   }  
  
   // Create an accessor from the set of bindings (pBindings).  
   pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA, lNumCols, pBindings, 0, &hAccessor, NULL);  
  
   // Print column names.  
   for ( j = 0 ; j < lNumCols ; j++ )  
      printf("%-40S", pDBColumnInfo[j].pwszName);  
  
   printf("\n");   // new line after the column names  
  
   // Get a set of 10 rows.  
   pIRowset->GetNextRows( NULL, 0, 10, &lNumRowsRetrieved, &pRows);  
  
   // Allocate space for the row buffer.  
   BYTE * pBuffer = new BYTE[ConsumerBufColOffset];  
   if (!(pBuffer /* = new BYTE[ConsumerBufColOffset] */ )) {  
      // Free up all allocated memory.  
      pIAccessor->ReleaseAccessor(hAccessor, NULL);  
      pIAccessor->Release();  
      delete [] pBindings;  
  
      return 0;  
   }  
  
   // Create an instance of the data conversion library to convert DBTYPE_CY to string for display  
   IDataConvert* pIDataConvert;  
   CoCreateInstance(CLSID_OLEDB_CONVERSIONLIBRARY,  
      NULL,  
      CLSCTX_INPROC_SERVER,  
      IID_IDataConvert,  
      (void**)&pIDataConvert);  
  
   // variables used in DataConvert  
   DBLENGTH cbDstLength;  
   DBSTATUS dbsStatus;  
   char strCurrency0[25];  
   char strCurrency1[25];  
  
   // Display the rows.  
   while ( lNumRowsRetrieved > 0 ) {  
      // For each row, print the column data.  
      for ( j = 0 ; j < lNumRowsRetrieved ; j++ ) {  
         // Clear the buffer.  
         memset(pBuffer, 0, ConsumerBufColOffset);  
  
         // Get the row data values.  
         pIRowset->GetData(hRows[j], hAccessor, pBuffer);  
  
         // Convert DBTYPE_CY values to string   
         pIDataConvert->DataConvert(DBTYPE_CY,   // wSrcType  
            DBTYPE_STR,   // wDstType  
            sizeof(LARGE_INTEGER),   // cbSrcLength   
            &cbDstLength,   // pcbDstLength  
            &pBuffer[pBindings[0].obValue],   // pSrc  
            strCurrency0,   // pDst  
            sizeof(strCurrency0),   //cbDstMaxLength  
            DBSTATUS_S_OK,   // dbsSrcStatus  
            &dbsStatus,   // pdbsStatus  
            0,   // bPrecision (used for DBTYPE_NUMERIC only)  
            0,   // bScale (used for DBTYPE_NUMERIC only)  
            DBDATACONVERT_DEFAULT);   // dwFlags  
  
         pIDataConvert->DataConvert(DBTYPE_CY,   // wSrcType  
            DBTYPE_STR,   // wDstType  
            sizeof(LARGE_INTEGER),   // cbSrcLength   
            &cbDstLength,   // pcbDstLength  
            &pBuffer[pBindings[1].obValue],   // pSrc  
            strCurrency1,   // pDst  
            sizeof(strCurrency1),   // cbDstMaxLength  
            DBSTATUS_S_OK,   // dbsSrcStatus  
            &dbsStatus,   // pdbsStatus  
            0,   // bPrecision (used for DBTYPE_NUMERIC only)  
            0,   // bScale (used for DBTYPE_NUMERIC only)  
            DBDATACONVERT_DEFAULT); // dwFlags  
  
         // Print cost and price values.  
         printf("%-40s%s\n", strCurrency0, strCurrency1); //sparra  
      };  
  
      // Release the rows retrieved.  
      pIRowset->ReleaseRows(lNumRowsRetrieved, hRows, NULL, NULL, NULL);  
  
      // Get the next set of 10 rows.  
      pIRowset->GetNextRows(NULL, 0, 10, &lNumRowsRetrieved, &pRows);  
   }  
  
   // Free up all allocated memory.  
   delete [] pBuffer;  
   pIAccessor->ReleaseAccessor(hAccessor, NULL);  
   pIAccessor->Release();  
   delete [] pBindings;  
  
   return 0;  
}  

Vedi anche

Procedure relative all'elaborazione dei risultati (OLE DB)