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Not sure if there is something wrong in my brain but I have not been able to understand the hate against NULL. To me the three value logic feels very natural an

Not sure if there is something wrong in my brain but I have not been able to understand the hate against NULL. To me the three value logic feels very natural and just clicks. Lately I have been dipping my toes into Alteryx, which treats empty values in a way that definitely does not correspond to 'normal' NULL logic in databases and it feels very much like a constraint on building my workflows.

vpetrovykh 7y ago
If a NULL were just a value in 3-valued logic, it could have been OK. However, that's not how it works out. Consider the following (that should be equivalent if NULL is just like Maybe in True-Maybe-False logic): SELECT null AND true; SELECT bool_and(column1) FROM (VALUES (null::bool),(true)) AS foo; In PostgreSQL the first query produces NULL, while the second produces TRUE. Yet, it's also possible to get NULL as a result of aggregating values with bool_and: SELECT bool_and(column1) FROM (VALUES (null::bool),(null::bool)) AS foo; And that's not how a 3-valued logic works.
- MarkusWinand 7y ago
  You are mixing two concepts here: 3VL and how most aggregates work in SQL: the drop NULL values before doing their work. That's why the first BOOL_AND example only sees one value, thus returning true.