取得大型資料

適用於：SQL Server Azure SQL 資料 Azure SQL 受控執行個體 Azure Synapse Analytics Analytics Platform System (PDW)

下載 OLE DB 驅動程式

一般而言，取用者應該隔離的程式碼會從處理不透過 ISequentialStream 介面指標參照之資料的其他程式碼，建立 OLE DB Driver for SQL Server 儲存物件。

本文是指下列函式提供的功能：

• IRowset:GetData

• IRow::GetColumns

• ICommand::Execute

如果 DBPROP_ACCESSORDER 屬性 (在資料列集屬性群組中) 設定為 DBPROPVAL_AO_SEQUENTIAL 或 DBPROPVAL_AO_SEQUENTIALSTORAGEOBJECTS，取用者應該在 GetNextRows 方法的呼叫中，僅提取資料的單一資料列。 這是因為 BLOB 資料不會經過緩衝處理。 如果 DBPROP_ACCESSORDER 的值設定為 DBPROPVAL_AO_RANDOM，取用者可以在 GetNextRows 中提取資料的多個資料列。

在取用者要求之前，OLE DB Driver for SQL Server 不會從 SQL Server 擷取大型資料。 取用者應該在一個存取子中繫結所有短資料，然後在需要時，使用一或多個暫存的存取子來擷取大型資料值。

範例

此範例會從單一資料行擷取大型資料值：

HRESULT GetUnboundData  
    (  
    IRowset* pIRowset,  
    HROW hRow,  
    ULONG nCol,   
    BYTE* pUnboundData  
    )  
    {  
    UINT                cbRow = sizeof(IUnknown*) + sizeof(ULONG);  
    BYTE*               pRow = new BYTE[cbRow];  
  
    DBOBJECT            dbobject;  
  
    IAccessor*          pIAccessor = NULL;  
    HACCESSOR           haccessor;  
  
    DBBINDING           dbbinding;  
    ULONG               ulbindstatus;  
  
    ULONG               dwStatus;  
    ISequentialStream*  pISequentialStream;  
    ULONG               cbRead;  
  
    HRESULT             hr;  
  
    // Set up the DBOBJECT structure.  
    dbobject.dwFlags = STGM_READ;  
    dbobject.iid = IID_ISequentialStream;  
  
    // Create the DBBINDING, requesting a storage-object pointer from  
    // The OLE DB Driver for SQL Server.  
    dbbinding.iOrdinal = nCol;  
    dbbinding.obValue = 0;  
    dbbinding.obStatus = sizeof(IUnknown*);  
    dbbinding.obLength = 0;  
    dbbinding.pTypeInfo = NULL;  
    dbbinding.pObject = &dbobject;  
    dbbinding.pBindExt = NULL;  
    dbbinding.dwPart = DBPART_VALUE | DBPART_STATUS;  
    dbbinding.dwMemOwner = DBMEMOWNER_CLIENTOWNED;  
    dbbinding.eParamIO = DBPARAMIO_NOTPARAM;  
    dbbinding.cbMaxLen = 0;  
    dbbinding.dwFlags = 0;  
    dbbinding.wType = DBTYPE_IUNKNOWN;  
    dbbinding.bPrecision = 0;  
    dbbinding.bScale = 0;  
  
    if (FAILED(hr = pIRowset->  
        QueryInterface(IID_IAccessor, (void**) &pIAccessor)))  
        {  
        // Process QueryInterface failure.  
        return (hr);  
        }  
  
    // Create the accessor.  
    if (FAILED(hr = pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA, 1,  
        &dbbinding, 0, &haccessor, &ulbindstatus)))  
        {  
        // Process error from CreateAccessor.  
        pIAccessor->Release();  
        return (hr);  
        }  
  
    // Read and process BLOCK_SIZE bytes at a time.  
    if (SUCCEEDED(hr = pIRowset->GetData(hRow, haccessor, pRow)))  
        {  
        dwStatus = *((ULONG*) (pRow + dbbinding.obStatus));  
  
        if (dwStatus == DBSTATUS_S_ISNULL)  
            {  
            // Process NULL data  
            }  
        else if (dwStatus == DBSTATUS_S_OK)  
            {  
            pISequentialStream = *((ISequentialStream**)   
                (pRow + dbbinding.obValue));  
  
            do  
                {  
                if (SUCCEEDED(hr =  
                    pISequentialStream->Read(pUnboundData,  
                    BLOCK_SIZE, &cbRead)))  
                    {  
                    pUnboundData += cbRead;  
                    }  
                }  
            while (SUCCEEDED(hr) && cbRead >= BLOCK_SIZE);  
  
            pISequentialStream->Release();  
            }  
        }  
    else  
        {  
        // Process error from GetData.  
        }  
  
    pIAccessor->ReleaseAccessor(haccessor, NULL);  
    pIAccessor->Release();  
    delete [] pRow;  
  
    return (hr);  
    }  

另請參閱

BLOB 與 OLE 物件
使用大型實值型別