Beginning SQL

MemberId
1
10
14
6
5
8
7
11
15
4
13
12
9
The table represents every single row in the MemberDetails table; indeed, MemberId < ALL (SELECT
FilmId FROM Films WHERE FilmId > 99) has evaluated to true every time due to an empty results
set returned by the subquery.
That completes the look at the related operators ANY, SOME, and ALL. The next section continues the discussion
of using operators with subqueries by examining the EXISTS operator.
Using the EXISTS Operator
The EXISTS operator is unusual in that it checks for rows and does not compare columns. So far you’ve
seen lots of clauses that compare one column to another. On the other hand, EXISTS simply checks to see
whether a subquery has returned one or more rows. If it has, then the clause returns true; if not, then it
returns false.
This is best demonstrated with three very simple examples:
SELECT City
FROM Location
WHERE EXISTS (SELECT * FROM MemberDetails WHERE MemberId < 5);
SELECT City
FROM Location
WHERE EXISTS (SELECT * FROM MemberDetails WHERE MemberId > 99);
SELECT City
FROM Location
WHERE EXISTS (SELECT * FROM MemberDetails WHERE MemberId = 15);
Queries within Queries
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