SQL: Selecting the Highest Value Linked to a Title

In this article, we will delve into the world of SQL queries and explore how to select the highest value linked to a title. This involves joining two tables and manipulating the results to get the desired output.

Background

To understand the problem at hand, let’s first examine the given tables:

Book Table

Publisher Table

We want to select the highest revenue for each book title and its corresponding publisher.

Understanding the Query

The given query attempts to solve the problem but has a flaw. It calculates the total revenue for each book, including the price multiplied by sold, which may not be the desired outcome. We need to adjust the query to get only the highest value linked to a title.

The Problem with the Given Query

Let’s examine the given query:

SELECT b.titel, p.name, max(b.price*b.sold) as 'Revenue'
FROM publisher p, book b
WHERE p.code = b.publisher

This query calculates the total revenue for each book by multiplying price and sold. However, this is not the highest value linked to a title. We need to modify the query to get only the highest revenue.

Solution 1: Using a Single Query

One way to solve this problem is to use a single query with an aggregate function:

SELECT b.titel, p.name, max(b.price*b.sold) as 'Revenue'
FROM publisher p, book b
WHERE p.code = b.publisher
GROUP BY b.titel, p.name

However, this query will return all books along with their highest revenue. We want to get only the title and its corresponding publisher for the highest revenue.

Solution 2: Using a Subquery

A better approach is to use a subquery to first calculate the highest revenue for each book title and then select only those results:

SELECT b.titel, p.name
FROM publisher p, book b
WHERE p.code = b.publisher
AND (b.title, p.name) IN (
  SELECT b.titel, p.name
  FROM publisher p, book b
  WHERE p.code = b.publisher
  GROUP BY b.titel, p.name
  ORDER BY max(b.price*b.sold) DESC
)

This query uses a subquery to calculate the highest revenue for each book title and then selects only those results where the revenue is the highest.

Solution 3: Using Window Functions

Another way to solve this problem is by using window functions, which allow us to calculate the ranking of rows within a result set:

SELECT b.titel, p.name,
       max(b.price*b.sold) OVER (PARTITION BY b.title ORDER BY max(b.price*b.sold) DESC) as 'Revenue'
FROM publisher p, book b
WHERE p.code = b.publisher

However, this query will return all books along with their highest revenue. We want to get only the title and its corresponding publisher for the highest revenue.

Solution 4: Using CTEs (Common Table Expressions)

CTEs are a powerful feature in SQL that allow us to define temporary result sets that can be referenced within a SELECT, INSERT, UPDATE, or DELETE statement:

WITH ranked_books AS (
  SELECT b.titel, p.name,
         max(b.price*b.sold) OVER (PARTITION BY b.title ORDER BY max(b.price*b.sold) DESC) as 'Revenue'
  FROM publisher p, book b
  WHERE p.code = b.publisher
)
SELECT title, name
FROM ranked_books
WHERE Revenue = (SELECT MAX(Revuee) FROM ranked_books);

This query uses a CTE to calculate the highest revenue for each book title and then selects only those results where the revenue is the highest.

Conclusion

In this article, we explored how to select the highest value linked to a title in SQL. We discussed several approaches, including using aggregate functions, subqueries, window functions, and CTEs. Each approach has its own advantages and disadvantages, and the choice of which one to use depends on the specific requirements of the problem at hand.

We hope this article has provided you with a deeper understanding of how to solve similar problems in SQL. If you have any further questions or need more clarification on any of the concepts discussed, feel free to ask!

Last modified on 2023-07-31