An easy way to think about database nulls is how you would answer a question in real life about unknowns.
I have a friend James, and another friend Jane. I don't know their ages. Are they of the same age?
Or Jane has a car. James has a blue car. Do car colours differ?
SQL provides human answers: explicitly answers "I don't know".
Other languages treat null as if it was just another value, providing very confusing answers. I wish all programming languages would use SQL style of null.
I have a friend James, and another friend Jane. I don't know their ages. Are they of the same age?
Or Jane has a car. James has a blue car. Do car colours differ?
SQL provides human answers: explicitly answers "I don't know".
Other languages treat null as if it was just another value, providing very confusing answers. I wish all programming languages would use SQL style of null.