Working of ANY and ALL with empty set

Question

create table stud(id int, grade varchar(20));

insert into stud values(1, 'A');
insert into stud values(2, 'A');
insert into stud values(3, 'B');
insert into stud values(4, 'B');

// Working of ALL : >=ALL, =ALL, >ALL : All the combinations Returning all rows

Select id from stud s WHERE s.grade =ALL (Select grade from stud e WHERE
e.id = 5);

// Working of ANY : >ANY, =ANY, >=ANY : All the combinations Returning no rows

Select id from stud s WHERE s.grade >ANY (Select grade from stud e WHERE e.id = 5);

Why is ANY and ALL behaving differently? Following are the queries -

I think the inner subquery rerturns NOTHING and NOT a null. Is that an empty set?

How is ANY and ALL deciding their output with respect to empty set?

Comments

please format using editor addcode option ..sql is avalable

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• ALL condition becomes false only when there is something that invalidates the criteria
• ANY condition becomes true only when there is something that validates the criteria

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By applying above logic ALL and ANY function working with null set behavior can be understood. 

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Yes thanks a lot @Debashish for the logic. I got the logic behind the working.

Answer 1

Irrespective of operand, op ALL(empty Set) is always TRUE and op ANY(empty Set) is always FALSE

In the first query , All nows will be selected and in the query, no row will be selected.

Answer 2

ALL (1 st condition and 2nd and 3 rd.. ) than ALL becomes True .

ANY(1st condition OR 2nd OR 3rd....) if not any than return false.