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