Filtering the groups
The Metropolitan Public Library's new rating statistics feature is a hit! However, patrons have complained that books with only one or two reviews can have misleading averages. A book with a single 5-star review appears just as highly rated as a beloved classic with hundreds of positive reviews.
The library director has asked you to enhance the system by allowing users to filter out books with insufficient reviews.
This exercise is part of the course
Querying a PostgreSQL Database in Java
Exercise instructions
- Complete the query to filter books with a specified number of reviews.
- Securely set the parameter only to display books with at least three reviews.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
public class Main {
public static void main(String[] args) throws SQLException {
HikariDataSource ds = HikariSetup.createDataSource();
String query = """
SELECT book_id, COUNT(*), AVG(rating)
FROM book_reviews
GROUP BY book_id
-- Filter books with a specified number of reviews
____ count(*) >= ?
""";
try (Connection conn = ds.getConnection();
PreparedStatement pstmt = conn.prepareStatement(query)) {
// Display books with at least three reviews
pstmt.____(____, ____);
try (ResultSet rs = pstmt.executeQuery()) {
while (rs.next()) {
System.out.printf("ID: %d, Count: %d, Average: %.0f%n",
rs.getInt("book_id"), rs.getInt("count"), rs.getDouble("avg"));
}
}
}
}
}