> Since it’s possible to hash multiple items to the same
> indices, a membership test returns either false or maybe.
True Positive: Test was correctly passed, hit. False Positive: Test was incorrectly passed, false alarm. True Negative: Test was correctly failed, reject. False Negative: Test was incorrectly failed, miss.
I find the terms to be too technical, so I remember a common situation. Medical tests are often False Positives. Which means the test was positive, but the test was wrong and you are okay (good!). From there is pretty easy to infer the rest.
Infact, that situation leads to a large issue with medical testing at a whole. If you were tested for 100 terrible diseases that you did not have, you would probably get a bunch of False Positives. Medical tests are set up for a high False Positive rate but low False Negative rate, because its less damaging to confirm a diagnosis with follow up testing than to miss a test. But confirming False Positive tests is expensive, along with the initial testing. So doctors try to limit tests to at-risk groups to spend less time on healthy patients' False Positive tests.
If a boolean value is null in SQL, it conceptually means it could be either true or false - it's a maybe. If you ask "is maybe true equal to maybe true", the answer is "maybe". Likewise, asking SQL 'null = null", it answers "null", instead of true/false.
SQL null IS nullThat's hard to explain when you work with binary booleans.