Example of three valued logic in SQL Server

Question

I understand that SQL uses three valued logic but I am having trouble understanding how to use this in practice, especially why TRUE || NULL = True and FA

Answer 1

The code example by user4955163 is a great visualization of this, however I just wanted to step back in to address the first segment of the question:

...especially why TRUE || NULL = True and FALSE && NULL = False instead of evaluating to null...

TRUE || NULL = True

This is because the or operator will short-circuit if one operand is already known to be true. No matter what the second operand is (even if unknown, ie. "NULL"), it wouldn't make the expression false since we already know the other operand is true. or only needs one operand to be true, to evaluate to true.

FALSE && NULL = False

This is because the and operator will short-circuit if one operand is already known to be false. No matter what the second operand is (even if unknown, ie. "NULL"), it wouldn't make the expression true since we already know the other operand is false. and needs both operands to be true to evaluate to true.