a) If a query/subquery doesn’t find any matching rows, then it either returns NULL or no value at all, thus not even a NULL value. Based on what criteria does a query/subquery return a NULL and when doesn’t it return any results, not even a NULL value?

b) I assume a scalar subquery will always return NULL, when no matching rows are found? I assume most-outer scalar query also returns NULL if no rows are found?

c)

SELECT FirstName, LastName, YEAR(BirthDate)
FROM Persons
WHERE YEAR(BirthDate) IN (SELECT YearReleased FROM Albums);

• If subquery finds no results, is then a WHERE clause of an outer query translated into WHERE YEAR(BirthDate) IN (null); ?

• If instead WHERE clause is translated into WHERE YEAR(BirthDate) IN(); then shouldn’t that be an error condition, since how can YEAR(BirthDate) value be compared to nothing?

thanx