Is there a recommended way to indicate whether a field in a record of
a table is invalid? For example, for double's, I could use NaN. But
that does not work if I actually want to store a NaN. Also, I need
something that works for everything: strings, bools, etc. I could do
it by adding a char array column and checking the bit corresponding to
a column. It is a bit clunky, and I want to make sure I am not
reinventing the wheel.