UPDATE .WRITE最后添加额外的字节

Question

当我运行这段代码时，我需要运行最后一条SQL语句来从blob中删除一个空字节。为什么我在FileBytes（varchar（max））字段的末尾有这个空字节是没有意义的。

代码有效。出于好奇，为什么我需要最后一个语句来摆脱空字节。或者我错过了为什么它在那里。

这是我的代码。

    public static void SaveBlob(DbConnection connection, DbTransaction trans, Guid attachmentGuid, Stream stream)
    {
        int bufferLen = 8040; //Recommended size from MSDN (multiples of 8040)

        string sql = "UPDATE Attachments ";
        sql += "SET FileBytes .WRITE(@Bytes, @Offset, 0) ";
        sql += "WHERE Attachments.AttachmentGUID = @AttachmentGUID";

        using (DbCommand command = connection.CreateCommand())
        {
            command.Transaction = trans;
            command.CommandText = sql;

            // Read the image in and write it to the database 128 (bufferLen) bytes at a time.
            // Tune bufferLen for best performance. Larger values write faster, but
            // use more system resources.
            BinaryReader br = new BinaryReader(stream);

            byte[] buffer = br.ReadBytes(bufferLen);                

            int offset = 0;
            DbParameter blobParam = command.AddParameter("@Bytes", stream);
            blobParam.Size = buffer.Length;
            DbParameter offsetParam = command.AddParameter("@Offset", offset);
            command.AddParameter("@AttachmentGUID", attachmentGuid);

            int offset_ctr = 0;

            while (buffer.Length > 0)
            {
                blobParam.Size = buffer.Length;
                blobParam.Value = buffer;
                command.ExecuteNonQuery();
                offset_ctr += bufferLen;
                offsetParam.Value = offset_ctr;

                buffer = br.ReadBytes(bufferLen);
            }

            //Need one more
            //Removes last byte (empty and extra)
            //I do not understand why I need this
            sql = "UPDATE Attachments ";
            sql += "SET FileBytes .WRITE(NULL, " + stream.Length.ToString() + @", 1) ";
            sql += "WHERE Attachments.AttachmentGUID = @AttachmentGUID ";
            sql += "AND DATALENGTH(FileBytes) > " + stream.Length.ToString();

            command.CommandText = sql;
            command.Parameters.Clear();
            command.AddParameter("@AttachmentGUID", attachmentGuid);
            command.ExecuteNonQuery();


            br.Close();
        }            
    }