with Query do
begin
  SQL.Clear;
  SQL.Add('update test.test');
  SQL.Add('set test=:test');
  SQL.Add('where id=1');
  ParamByName('test').LoadFromFile('d:\1.txt', ftBlob);
  ExecSQL;
end;

with Query do
begin
  SQL.Clear;
  SQL.Add('SELECT test FROM test.test');
  SQL.Add('where id=1');
  Open;
  try
    if (not eof) then
    begin
      (FieldByName('test') as TBlobField).SaveToFile('d:\2.txt');
    end;
  finally
    Close;
  end;
end;