Using large value types

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW)

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Before SQL Server 2005 (9.x), working with large value data types required special handling. Large value data types are the types that exceed the maximum row size of 8 KB. SQL Server 2005 (9.x) introduced a max specifier for varchar, nvarchar, and varbinary data types to allow storage of values as large as 2^31 -1 bytes. Table columns and Transact-SQL variables may specify varchar(max), nvarchar(max), or varbinary(max) data types.

Previously, only SQL Server data types such as text, ntext, and image could be so large. The max specifier for varchar, nvarchar, and varbinary made these data types redundant. However, because long data types are still available, most of the interfaces to the OLE DB data access components will remain the same. For backward compatibility with prior releases, the DBCOLUMNFLAGS_ISLONG flag in the OLE DB Driver for SQL Server remains in use. Providers and drivers written against SQL Server 2005 (9.x) and later continue to use these terms for the new types when set to unlimited maximum length.

OLE DB Driver for SQL Server

The OLE DB Driver for SQL Server exposes the varchar(max), varbinary(max), and nvarchar(max) types as DBTYPE_STR, DBTYPE_BYTES, and DBTYPE_WSTR, respectively.

The data types varchar(max), varbinary(max), and nvarchar(max) in columns with the max size set to unlimited are represented as an ISLONG through the core OLE DB schema rowsets and interfaces that return column data types.

The command object's IAccessor implementation has been changed to allow binding as DBTYPE_IUNKNOWN. If the consumer specifies DBTYPE_IUNKNOWN and sets pObject to null, the provider will return the ISequentialStream interface to the consumer so that the consumer can stream varchar(max), nvarchar(max), or varbinary(max) data out of output variables.

Streamed output parameter values are returned after any result rows. If the application attempts to move on to the next result set by calling IMultipleResults::GetResult without consuming all the returned output parameter values, DB_E_OBJECTOPEN will be returned.

In order to support streaming, the OLE DB Driver for SQL Server requires variable length parameters to be accessed in sequential order. This requirement means that DBPROP_ACCESSORDER must be set to either DBPROPVAL_AO_SEQUENTIALSTORAGEOBJECTS or DBPROPVAL_AO_SEQUENTIAL whenever varchar(max), nvarchchar(max), or varbinary(max) columns or output parameters are bound to DBTYPE_IUNKNOWN. Calls to IRowset::GetData will fail with DBSTATUS_E_UNAVAILABLE if this access order restriction is not adhered to. This restriction does not apply when there are no output bindings using DBTYPE_IUNKNOWN.

The OLE DB Driver for SQL Server also supports binding output parameters as DBTYPE_IUNKNOWN for large value data types to facilitate scenarios where a stored procedure returns large value types as return values that are exposed as DBTYPE_IUNKNOWN to the client.

To work with these types, an application has the following options:

• Bind as a type that has supported bindings with the base type of the column (for example, for nvarchar(max), bind as a type that can be bound to nvarchar). If the buffer is not large enough truncation will occur, exactly as for the base type, albeit that larger values are now available.
• Bind as a type that has supported conversions with the base type of the column and also specify DBTYPE_BYREF.
• Bind as DBTYPE_IUNKNOWN and use streaming.

When reporting the maximum size of a column, the OLE DB Driver for SQL Server will report:

• The defined maximum size, which, for example, is 2000 for a varchar(2000) column, or
• The value "unlimited", which for a varchar(max) column equals ~0. This value is set for the DBCOLUMN_COLUMNSIZE metadata property.

The standard conversion rules will apply to a varchar(max) column, meaning that any conversion that is valid for a varchar(2000) column will also be valid for a varchar(max) column. The same is true for nvarchar(max) and varbinary(max) columns.

When retrieving large value types, the most efficient approach is to bind as DBTYPE_IUNKNOWN and set the rowset property DBPROP_ACCESSORDER to DBPROPVAL_AO_SEQUENTIALSTORAGEOBJECTS. This setting will cause the value to be streamed directly from the network with no intermediate buffering, as in the following example:

#define UNICODE
#define _UNICODE
#define DBINITCONSTANTS
#define INITGUID
#define OLEDBVER 0x0250  // To include the correct interfaces.

#include <stdio.h>
#include <tchar.h>
#include <stddef.h>
#include <iostream>

using std::cout;
using std::endl;

#include <windows.h>

#include <oledb.h>
#include "msoledbsql.h"
#include <oledberr.h>

#define CHKHR_GOTO(hr, errMsg, Label) \
   if (FAILED(hr)) \
   { \
      cout << errMsg << endl; \
      goto Label; \
   }

#define MAX_COL_SIZE 8000

// ROUNDUP on all platforms pointers must be aligned properly.
#define ROUNDUP_AMOUNT 8
#define ROUNDUP_(size,amount) (((ULONG)(size)+((amount)-1))&~((amount)-1))
#define ROUNDUP(size) ROUNDUP_(size, ROUNDUP_AMOUNT)

HRESULT InitializeAndEstablishConnection(IDBInitialize** ppIDBInitialize);
void UnInitializeConnection(IDBInitialize* pIDBInitialize);
HRESULT CreateAndSetCommand(IDBInitialize* pIDBInitialize, ICommandText** ppICommandText);
HRESULT ProcessResultSet(IRowset* pIRowset);

void DisplayTime()
{
   SYSTEMTIME st;
   GetSystemTime(&st);
   cout<< st.wHour << ":" << st.wMinute << ":" << st.wSecond << "." << st.wMilliseconds << endl;
}

void main()
{
   HRESULT hr;
   IDBInitialize* pIDBInitialize = NULL;
   ICommandText* pICommandText = NULL;
   IMultipleResults* pIMultipleResults = NULL;
   IRowset* pIRowset = NULL;

   hr = InitializeAndEstablishConnection(&pIDBInitialize);
   CHKHR_GOTO(hr, L"Failed to establish connection.", _ExitMain);

   hr = CreateAndSetCommand(pIDBInitialize, &pICommandText);
   CHKHR_GOTO(hr, L"Failed to set up command object.", _ExitMain);

   DisplayTime();

   hr = pICommandText->Execute(NULL,
      IID_IMultipleResults,
      NULL,
      NULL,
     (IUnknown **) &pIMultipleResults);

   CHKHR_GOTO(hr, L"Failed to execute command.", _ExitMain);

   while (1)
   {
      hr = pIMultipleResults->GetResult(
         NULL,
         DBRESULTFLAG_DEFAULT,
         IID_IRowset,
         NULL,
         (IUnknown**)&pIRowset);

   CHKHR_GOTO(hr, L"Failed to obtain a results from MR object.", _ExitMain);

   if (hr == DB_S_NORESULT)
      break;

      if (pIRowset)
      {
         hr = ProcessResultSet(pIRowset);
         CHKHR_GOTO(hr, L"Failed to process the current Rowset.", _ExitMain);

         pIRowset->Release();
         pIRowset = NULL;
      }
   }

   DisplayTime();

_ExitMain:

   if (pIRowset)
   {
      pIRowset->Release();
      pIRowset = NULL;
   }

   if (pIMultipleResults)
   {
      pIMultipleResults->Release();
      pIMultipleResults = NULL;
   }

   if (pICommandText)
   {
      pICommandText->Release();
      pICommandText = NULL;
   }

   UnInitializeConnection(pIDBInitialize);
   return;
};

HRESULT InitializeAndEstablishConnection(IDBInitialize** ppIDBInitialize)
{
   HRESULT hr;
   IDBInitialize* pIDBInitialize = NULL;
   IDBProperties* pIDBProperties = NULL;

   const int NUM_DBINIT_PROPS = 3;
   const wchar_t* const g_wszServer = L".";
   const wchar_t* const g_wszCatalog = L"AdventureWorks";
   const wchar_t* const g_wszSecurity = L"SSPI";

   DBPROPSET rgdbPropSetInit[1];
   DBPROP rgdbPropInit [NUM_DBINIT_PROPS];

   *ppIDBInitialize = NULL;
   hr = CoInitialize(NULL);
   CHKHR_GOTO(hr, L"Failed to initialize COM.", _ExitInitialize);

   hr = CoCreateInstance(CLSID_MSOLEDBSQL,
      NULL,
      CLSCTX_INPROC_SERVER,
      IID_IDBInitialize,
      (void**)&pIDBInitialize);

   CHKHR_GOTO(hr, L"Failed to create MSOLEDBSQL DataSource object.", _ExitInitialize);

   for(int idxProp = 0; idxProp < NUM_DBINIT_PROPS; idxProp++)
   {
      VariantInit(&rgdbPropInit[idxProp].vValue);
   }

   rgdbPropInit[0].dwPropertyID = DBPROP_INIT_DATASOURCE;
   rgdbPropInit[0].vValue.vt = VT_BSTR;
   rgdbPropInit[0].vValue.bstrVal= SysAllocString(g_wszServer);
   rgdbPropInit[0].dwOptions = DBPROPOPTIONS_REQUIRED;
   rgdbPropInit[0].colid = DB_NULLID;

   if (rgdbPropInit[0].vValue.bstrVal == NULL)
   {
      hr = E_OUTOFMEMORY;
      goto _ExitInitialize;
   }

   rgdbPropInit[1].dwPropertyID = DBPROP_INIT_CATALOG;
   rgdbPropInit[1].vValue.vt = VT_BSTR;
   rgdbPropInit[1].vValue.bstrVal= SysAllocString(g_wszCatalog);
   rgdbPropInit[1].dwOptions = DBPROPOPTIONS_REQUIRED;
   rgdbPropInit[1].colid = DB_NULLID;

   if (rgdbPropInit[1].vValue.bstrVal == NULL)
   {
      hr = E_OUTOFMEMORY;
      goto _ExitInitialize;
   }

   rgdbPropInit[2].dwPropertyID = DBPROP_AUTH_INTEGRATED;
   rgdbPropInit[2].vValue.vt = VT_BSTR;
   rgdbPropInit[2].vValue.bstrVal= SysAllocString(g_wszSecurity);
   rgdbPropInit[2].dwOptions = DBPROPOPTIONS_REQUIRED;
   rgdbPropInit[2].colid = DB_NULLID;

   if (rgdbPropInit[2].vValue.bstrVal == NULL)
   {
      hr = E_OUTOFMEMORY;
      goto _ExitInitialize;
   }

   rgdbPropSetInit[0].guidPropertySet = DBPROPSET_DBINIT;
   rgdbPropSetInit[0].cProperties = NUM_DBINIT_PROPS;
   rgdbPropSetInit[0].rgProperties = rgdbPropInit;

   hr = pIDBInitialize->QueryInterface(IID_IDBProperties, (void **)&pIDBProperties);
   CHKHR_GOTO(hr, L"Failed to QI DataSource object for IDBProperties.", _ExitInitialize);

   hr = pIDBProperties->SetProperties(1, rgdbPropSetInit);
   CHKHR_GOTO(hr, L"Failed to set DataSource object Properties.", _ExitInitialize);

   pIDBProperties->Release();
   pIDBProperties = NULL;

   hr = pIDBInitialize->Initialize();
   CHKHR_GOTO(hr, L"Failed to establish connection with the server.", _ExitInitialize);

_ExitInitialize:

   if (pIDBProperties)
   {
      pIDBProperties->Release();
      pIDBProperties = NULL;
   }

   if (FAILED(hr))
   {
      if (pIDBInitialize)
      {
         pIDBInitialize->Release();
         pIDBInitialize = NULL;
      }
   }

   *ppIDBInitialize = pIDBInitialize;
   return hr;
}

void UnInitializeConnection(IDBInitialize* pIDBInitialize)
{
   if (pIDBInitialize)
   {
      pIDBInitialize->Uninitialize();
      pIDBInitialize->Release();
      pIDBInitialize = NULL;
   }
   CoUninitialize();
}

HRESULT CreateAndSetCommand(IDBInitialize* pIDBInitialize, ICommandText** ppICommandText)
{
   HRESULT hr;
   IDBCreateSession* pIDBCreateSession = NULL;
   IDBCreateCommand* pIDBCreateCommand = NULL;
   ICommandText* pICommandText = NULL;
   ICommandProperties* pICommandProperties = NULL;
   DBPROPSET rgCmdPropSet[1];
   DBPROP rgCmdProperties[1];

const wchar_t* const g_wCmdString = L"declare @x xml, @y nvarchar(max); select @x = (SELECT * FROM Sales.SalesOrderHeader FOR XML AUTO); select @x;";

   *ppICommandText = NULL;

   if (!pIDBInitialize)
   {
      hr = E_FAIL;
      goto _ExitCreateAndSetCommand;
   }

   hr = pIDBInitialize->QueryInterface(IID_IDBCreateSession, (void**) &pIDBCreateSession);
   CHKHR_GOTO(hr, L"Failed to obtain IDBCreateSession interface from DSO.", _ExitCreateAndSetCommand);

   hr = pIDBCreateSession->CreateSession(
      NULL,
      IID_IDBCreateCommand,
      (IUnknown**) &pIDBCreateCommand);

   CHKHR_GOTO(hr, L"Failed to Create a Session for command execution.", _ExitCreateAndSetCommand);

   hr = pIDBCreateCommand->CreateCommand(
      NULL,
      IID_ICommandText,
      (IUnknown**)&pICommandText);

   CHKHR_GOTO(hr, L"Failed to Create a Command object.", _ExitCreateAndSetCommand);

   hr = pICommandText->SetCommandText(DBGUID_DBSQL, g_wCmdString);
   CHKHR_GOTO(hr, L"Failed to Set Command Text.", _ExitCreateAndSetCommand);

   hr = pICommandText->QueryInterface(IID_ICommandProperties, (void**) &pICommandProperties);
   CHKHR_GOTO(hr, L"Failed to obtain ICommandProperties interface from the command object.", _ExitCreateAndSetCommand);

   rgCmdProperties[0].dwPropertyID = DBPROP_ACCESSORDER;
   rgCmdProperties[0].vValue.vt = VT_I4;
   rgCmdProperties[0].vValue.lVal = DBPROPVAL_AO_SEQUENTIAL;
   rgCmdProperties[0].dwOptions = DBPROPOPTIONS_REQUIRED;
   rgCmdProperties[0].colid = DB_NULLID;

   rgCmdPropSet[0].guidPropertySet = DBPROPSET_ROWSET;
   rgCmdPropSet[0].cProperties = 1;
   rgCmdPropSet[0].rgProperties = rgCmdProperties;

   hr = pICommandProperties->SetProperties(1, rgCmdPropSet);
   CHKHR_GOTO(hr, L"Failed to Set Command object Properties.", _ExitCreateAndSetCommand);

_ExitCreateAndSetCommand:

   if (pICommandProperties)
   {
      pICommandProperties->Release();
      pICommandProperties = NULL;
   }

   if (pIDBCreateCommand)
   {
      pIDBCreateCommand->Release();
      pIDBCreateCommand = NULL;
   }

   if (pIDBCreateSession)
   {
      pIDBCreateSession->Release();
      pIDBCreateSession = NULL;
   }

   if (FAILED(hr))
   {
      if (pICommandText)
      {
         pICommandText->Release();
         pICommandText = NULL;
      }
   }

   *ppICommandText = pICommandText;
   return hr;
}

HRESULT ProcessResultSet(IRowset* pIRowset)
{
   HRESULT hr;

   IColumnsInfo* pIColumnsInfo = NULL;
   DBCOLUMNINFO* pDBColumnInfo = NULL;
   ULONG lNumCols = 0;
   wchar_t* pStringsBuffer = NULL;

   DBBINDING* pBindings = NULL;
   DBOBJECT dbobj;
   ULONG idxBinding;
   IAccessor* pIAccessor = NULL;
   HACCESSOR hAccessor = DB_NULL_HACCESSOR;
   HROW hRows[1] = {DB_NULL_HROW};
   HROW* pRow = &hRows[0];
   BYTE* pBuffer = NULL;

   ULONG lNumRowsRetrieved;
   DBLENGTH dwOffset = 0;

   hr = pIRowset->QueryInterface(IID_IColumnsInfo, (void **)&pIColumnsInfo);
   CHKHR_GOTO(hr, L"Failed to QI Rowset for IColumnsInfo.", _ExitProcessResultSet);

   hr = pIColumnsInfo->GetColumnInfo(&lNumCols, &pDBColumnInfo, &pStringsBuffer);
   CHKHR_GOTO(hr, L"Failed to obtain Column Information.", _ExitProcessResultSet);

   pBindings = new DBBINDING[lNumCols];

   if (!pBindings)
   {
      hr = E_OUTOFMEMORY;
      goto _ExitProcessResultSet;
   }

   memset(pBindings, 0, sizeof(DBBINDING) * lNumCols);

   dbobj.dwFlags = STGM_READ;
   dbobj.iid = IID_ISequentialStream;

   for (idxBinding = 0; idxBinding < lNumCols; idxBinding++)
   {
      pBindings[idxBinding].iOrdinal = idxBinding + 1;
      pBindings[idxBinding].obStatus = dwOffset;
      pBindings[idxBinding].obLength = dwOffset + sizeof(DBSTATUS);
      pBindings[idxBinding].obValue = dwOffset + sizeof(DBSTATUS) + sizeof(DBLENGTH);

      pBindings[idxBinding].pTypeInfo = NULL;
      pBindings[idxBinding].pBindExt = NULL;
      pBindings[idxBinding].dwPart = DBPART_VALUE | DBPART_LENGTH | DBPART_STATUS;
      pBindings[idxBinding].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
      pBindings[idxBinding].eParamIO = DBPARAMIO_NOTPARAM;
      pBindings[idxBinding].bPrecision = pDBColumnInfo[idxBinding].bPrecision;
      pBindings[idxBinding].bScale = pDBColumnInfo[idxBinding].bScale;

      pBindings[idxBinding].cbMaxLen = 0;
      pBindings[idxBinding].wType = DBTYPE_WSTR;

   // Determine the maximum number of bytes required in our buffer to
   // contain the Unicode string representation of the provider's native
   // data type, including room for the NULL-termination character
   switch( pDBColumnInfo[idxBinding].wType )
   {
      case DBTYPE_NULL:
      case DBTYPE_EMPTY:
      case DBTYPE_I1:
      case DBTYPE_I2:
      case DBTYPE_I4:
      case DBTYPE_UI1:
      case DBTYPE_UI2:
      case DBTYPE_UI4:
      case DBTYPE_R4:
      case DBTYPE_BOOL:
      case DBTYPE_I8:
      case DBTYPE_UI8:
      case DBTYPE_R8:
      case DBTYPE_CY:
      case DBTYPE_ERROR:
      // When the above types are converted to a string, they
      // will all fit into 25 characters, so use that plus space
      // for the NULL-terminator.

      pBindings[idxBinding].cbMaxLen = (25 + 1) * sizeof(WCHAR);
      break;

      case DBTYPE_DECIMAL:
      case DBTYPE_NUMERIC:
      case DBTYPE_DATE:
      case DBTYPE_DBDATE:
      case DBTYPE_DBTIMESTAMP:
      case DBTYPE_GUID:
      // Converted to a string, the above types will all fit into
      // 50 characters, so use that plus space for the terminator.

      pBindings[idxBinding].cbMaxLen = (50 + 1) * sizeof(WCHAR);
      break;

      case DBTYPE_BYTES:
      // In converting DBTYPE_BYTES to a string, each byte
      // becomes two characters (e.g. 0xFF -> "FF"), so we
      // will use double the maximum size of the column plus
      // include space for the NULL-terminator.

      pBindings[idxBinding].cbMaxLen = (pDBColumnInfo[idxBinding].ulColumnSize * 2 + 1) * sizeof(WCHAR);
      break;

      case DBTYPE_STR:
      case DBTYPE_WSTR:
      case DBTYPE_BSTR:
      // Going from a string to our string representation,
      // we can just take the maximum size of the column,
      // a count of characters, and include space for the
      // terminator, which is not included in the column size.

      pBindings[idxBinding].cbMaxLen = (pDBColumnInfo[idxBinding].ulColumnSize + 1) * sizeof(WCHAR);
      break;

      default:
      // For any other type, we will simply use our maximum
      // column buffer size, since the display size of these
      // columns may be variable (e.g. DBTYPE_VARIANT) or
      // unknown (e.g. provider-specific types).
      pBindings[idxBinding].cbMaxLen = MAX_COL_SIZE;
      break;
   }

   // If the provider's native data type for this column is
   // DBTYPE_IUNKNOWN or this is a BLOB column and the user
   // has requested that we bind BLOB columns as ISequentialStream
   // objects, bind this column as an ISequentialStream object if
   // the provider supports our creating another ISequentialStream
   // binding.
   if(pDBColumnInfo[idxBinding].dwFlags & DBCOLUMNFLAGS_ISLONG)
   {
      pBindings[idxBinding].wType = DBTYPE_IUNKNOWN;

      pBindings[idxBinding].cbMaxLen = sizeof(ISequentialStream*);

      pBindings[idxBinding].pObject = (DBOBJECT *)CoTaskMemAlloc(sizeof(DBOBJECT));

      if (!pBindings[idxBinding].pObject)
      {
         hr = E_OUTOFMEMORY;
         goto _ExitProcessResultSet;
      }

      // Direct the provider to create an ISequentialStream
      // object over the data for this column.
      pBindings[idxBinding].pObject->iid = IID_ISequentialStream;

      // We want read access on the ISequentialStream
      // object that the provider will create for us
      pBindings[idxBinding].pObject->dwFlags = STGM_READ;
      }

      // Ensure that the bound maximum length is no more than the
      // maximum column size in bytes that we've defined.
      pBindings[idxBinding].cbMaxLen = min(pBindings[idxBinding].cbMaxLen, MAX_COL_SIZE);

      // Update the offset past the end of this column's data, so
      // that the next column will begin in the correct place in
      // the buffer.
      dwOffset = pBindings[idxBinding].cbMaxLen + pBindings[idxBinding].obValue;

      // Ensure that the data for the next column will be correctly
      // aligned for all platforms, or, if we're done with columns,
      // that if we allocate space for multiple rows that the data
      // for every row is correctly aligned.
      dwOffset = ROUNDUP(dwOffset);
   }

   hr = pIRowset->QueryInterface(IID_IAccessor, (void **) &pIAccessor);
   CHKHR_GOTO(hr, L"Failed to obtain Accessor interface", _ExitProcessResultSet);

   hr = pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA,
      lNumCols,
      pBindings,
      0,
      &hAccessor,
      NULL);

   CHKHR_GOTO(hr, L"Failed to create Accessor", _ExitProcessResultSet);
   for (idxBinding = 0; idxBinding < lNumCols; idxBinding++)
   {
      cout << pDBColumnInfo[idxBinding].pwszName << endl;
   }

   lNumRowsRetrieved = 0;

   hr = pIRowset->GetNextRows(
      NULL,
      0,
      1,
      &lNumRowsRetrieved,
      &pRow);

   CHKHR_GOTO(hr, L"Failed to fetch a row from the rowset", _ExitProcessResultSet);

   pBuffer = new BYTE[sizeof(DBSTATUS) + sizeof(DBLENGTH) + sizeof(IUnknown*)];

   if (!pBuffer)
   {
      hr = E_OUTOFMEMORY;
      goto _ExitProcessResultSet;
   }

   while(lNumRowsRetrieved && hr != DB_S_ENDOFROWSET)
   {
      memset(pBuffer, 0, sizeof(DBSTATUS) + sizeof(DBLENGTH) + sizeof(IUnknown*));

      hr = pIRowset->GetData(hRows[0], hAccessor, pBuffer);
      CHKHR_GOTO(hr, L"Failed to obtain row data", _ExitProcessResultSet);

      for (idxBinding = 0; idxBinding < lNumCols; idxBinding++)
      {
         if (pBindings[idxBinding].wType == DBTYPE_IUNKNOWN)
         {
            BYTE pbBuff[3000];
            ULONG cbNeeded = sizeof(pbBuff)/sizeof(BYTE);
            ULONG cbRead;
            ULONG cbReadTotal = 0;
            ISequentialStream* pISequentialStream = NULL;

            IUnknown* pIUnknown = *((IUnknown**)(pBuffer + pBindings[idxBinding].obValue));
            pIUnknown->QueryInterface(IID_ISequentialStream, (void**)&pISequentialStream);

            do
            {
               hr = pISequentialStream->Read(pbBuff, cbNeeded, &cbRead);
               cbReadTotal += cbRead;
            }
            while (SUCCEEDED(hr) && hr != S_FALSE && cbRead == cbNeeded);

               cout << "Total Bytes Read: " << cbReadTotal << endl;

               pISequentialStream->Release();
               pISequentialStream = NULL;
               pIUnknown->Release();
               pIUnknown = NULL;
            }
         }

         pIRowset->ReleaseRows(1, pRow, NULL, NULL, NULL);

         hr = pIRowset->GetNextRows(NULL,
            0,
            1,
            &lNumRowsRetrieved,
            &pRow);

         CHKHR_GOTO(hr, L"Failed to fetch a row from the rowset.", _ExitProcessResultSet);
   }

_ExitProcessResultSet:

   pIRowset->ReleaseRows(1, pRow, NULL, NULL, NULL);
   delete [] pBuffer;

   if (pIAccessor)
   {
      if (hAccessor != DB_NULL_HACCESSOR)
      {
         pIAccessor->ReleaseAccessor(hAccessor, NULL);
      }

      pIAccessor->Release();
      pIAccessor = NULL;
   }

   if (pBindings)
   {
      for (idxBinding = 0; idxBinding < lNumCols; idxBinding++)
      {
         if (pBindings[idxBinding].pObject)
         CoTaskMemFree(pBindings[idxBinding].pObject);
      }
   }

   delete [] pBindings;

   CoTaskMemFree(pDBColumnInfo);
   CoTaskMemFree(pStringsBuffer);

   if (pIColumnsInfo)
   {
      pIColumnsInfo->Release();
      pIColumnsInfo = NULL;
   }

   return hr;
}

For more information about how the OLE DB Driver for SQL Server exposes large value data types, see BLOBs and OLE Objects.

See also

OLE DB Driver for SQL Server Features