Re: use null or 0 in foreign key column, to mean "no value"?

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От David G. Johnston
Тема Re: use null or 0 in foreign key column, to mean "no value"?
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Msg-id CAKFQuwbKVZC1z9X4xWPkLM5G-=g5KZGY9JdF7vk9Em3+cBz16w@mail.gmail.com
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Ответ на use null or 0 in foreign key column, to mean "no value"?  (Robert Nikander <rob.nikander@gmail.com>)
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On Friday, June 26, 2015, Robert Nikander <rob.nikander@gmail.com> wrote:
So… is this bad DB design to use null to mean that an item has no color? Should I instead put a special row in `colors`, maybe with id = 0, to represent the “no color” value?  Or is there some way to make an index work with nulls and `is not distinct from`?

Not sure about getting is distinct to work with indexes but in this particular case I would add a "colorless" color to the table and make the column constraint not null.

I would also likely just make the text value the unique key and forget the surrogate integer key.

David J.

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