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I am not understanding this solution! >__<
especially the subquery: "select min(coins_needed) from Wands as w1 join Wands_Property as p1 on (w1.code = p1.code) where w1.power = w.power and p1.age = p.age".
WHY using "where w1.power = w.power and p1.age = p.age"?
Is this subquery retrieving the minimum price for each combo of "power" and "age"? if so, how is it doing it?
like, WHY is it referencing the values from outer query (for example, p.age and w.power do not belong to this subquery)?