Here is a series of videos by CJ Date on Relational Theory.

Introduction video

An Introduction to set theory (videos on O'Reilly website)

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Nullology (videos on O'Reilly website)

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Nulls, Three-Valued Logic, and Missing Information (videos on O'Reilly website)

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The Closed World Assumption (videos on O'Reilly website)

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View Updating (videos on O'Reilly website)

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