Can you explain in detail the meaning of "*" and "+"?

Question

Can you explain in detail the meaning of "*" and " "

Answer 1

*: NULL value or multiple values ​​are allowed;

+: NULL value is not allowed, there must be at least one, and of course there can be multiple;

This is the second The difference between them is that the length of * can start from 0, while the length of + must start from 1