DUM and DEE differences in SQL

Question

I would like to know the difference between DUM and DEE. Can anybody spot the difference with real world example?

Answer 1

Both of them are relations that has no attributes. A relation with no attributes can have one tuple that is "empty". So we can say:
DUM is the relation that has no attributes and no tuples. It plays the role of False.
DEE is the relation that has no attributes and a single tuple. It plays the role of True.

HTML table that represents DUM:

<table><thead></thead><tbody></tbody></table>

HTML table that represents DEE:

<table><thead></thead><tbody><tr></tr></tbody></table>