Beginning SQL

Chapter 8
248
The subquery (SELECT FilmId FROM Films WHERE FilmId > 5) returns the following values:
FilmId
6
7
8
9
10
11
12
13
14
15
Essentially, this means that the WHERE clause is as follows:
MemberId < ALL (6,7,8,9,10,11,12,13,14,15);
MemberId must be less than all of the listed values if the condition is to evaluate to true. The full results
for the example query are displayed in the following table:
MemberId
1
4
5
There is something to be aware of when using ALL: the situation when the subquery returns no results at
all. In this case, ALL will be true, which may seem a little weird, but it’s based on fundamental principles
of logic. So, if you change the subquery so that it returns no values and update the previous example,
you end up with the following code:
SELECT MemberId
FROM MemberDetails
WHERE MemberId < ALL (SELECT FilmId FROM Films WHERE FilmId > 99);
You know for a fact that there are no FilmIds with a value higher than 99, so the subquery returns an
empty set. However, the results set for the example is shown in the following table: