Beginning SQL

Clearly this query hasn’t returned just the duplicates. That’s because you need to add a link between the
subquery and the outer query. Remember, you want only those rows where the name is the same but the
StarId is different. You have the same names, but you need to add a link between the query and subquery
that ensures that the StarIds are different:
SELECT StarId, StarName, StarAge FROM FilmStars S1
WHERE StarName IN (SELECT StarName FROM FilmStars S2
WHERE S2.StarId < S1.StarId)
ORDER BY StarName;
In the preceding code, a clause is added to the subquery that ensures that only rows where the StarIds
are different between the subquery and outer query are returned. This is done by specifying that
S2.StarId — the subquery’s StarId column — should have a value that is less than the StarId column in
S1 (the outer query’s StarId table).
The ORDER BY clause is there only to make the results easier to read, and it isn’t needed for the final
DELETE query. When you run this query, you get the following results:
StarId StarName StarAge
3 Boris Carlot 102
6 Boris Carlot 102
7 Dusty Hoffperson 48
As you can see, the query has selected the unwanted duplicate data. Having confirmed that the query
works, you can now convert it to a DELETE statement:
DELETE FROM FilmStars
WHERE StarName IN
(SELECT StarName FROM FilmStars S2 WHERE S2.StarId < FilmStars.StarId);
All you have to do is change SELECT to DELETE. You can also remove the alias, as some database systems
don’t allow aliases with DELETE statements. In the subquery, S1 is changed to FilmStars, which
references the outer FilmStars table mentioned in the DELETE FROM statement. Execute the query and
you should find that three rows are deleted.
Chapter 10
Exercise 1 Solution
CREATE VIEW vFirstLastDOB AS
SELECT FirstName, LastName, DateOfBirth
FROM MemberDetails
Exercise Answers
387