Beginning SQL

Now NOT EXISTS returns true, and as a result the WHERE clause is also true. The final results are
shown in the following table:
City
Orange Town
Windy Village
Big City
These examples are very simple and, to be honest, not that realistic in terms of how EXISTS is used. One
issue with the examples is that the subqueries don’t link in any way with the outer SELECT query,
whereas normally you’d expect them to do so. The following Try It Out example is a lot more realistic.
The task is to find out which categories have been chosen by three or more members as their favorite category
of film, but these favorite categories must contain at least one film with a rating higher than 3.
Try It Out Using the EXISTS Operator
Build the necessary query by following these steps:
1. First of all, formulate a SELECT statement that returns the values you want. In this case, you just
want the Category from the Category table:
SELECT Category
FROM Category
2. Now you need to add a WHERE clause to ensure that you get only categories that have films
rated 4 or higher and that have also been selected as a favorite by three or more members.
SELECT Category
FROM Category
WHERE EXISTS (SELECT * FROM Films
WHERE Category.CategoryId = Films.CategoryId
AND Rating > 3
)
Queries within Queries
3. Finally, you just want categories that three or more members have chosen as their favorite.
SELECT Category
FROM Category
WHERE EXISTS (SELECT * FROM Films
WHERE Category.CategoryId = Films.CategoryId
AND Rating > 3
AND (SELECT COUNT(CategoryId)
FROM FavCategory
WHERE FavCategory.CategoryId = Category.CategoryId)
>= 3
);
251