> No, actually, the table could ONLY have rows for the "checked"
> items.
>
> If there's no row, it's unchecked.
>

Martijn,

So NULL means False?

Most surveys I have seen (particularly with 600 checkboxes) are not
all compulsory. Sometimes only a few (random) questions are asked.

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25. Do you use firebird? (Y/N) (if so skip to question 50)
26. Do you like paying money for something that a free product does
better?

;)

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To me, it makes more sense to include a record for each answer, as
well as the answer given unless all questions are compulsory (where
you could save a bit of data storage). It may be important to
distinguish between the questions that have not been asked and the
questions they answered no to.

My 2c

Adam