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Today, we delve into a couple of SQL questions that will challenge your understanding of database querying and manipulation. Whether you're a beginner or an advanced learner, these exercises are designed to sharpen your SQL prowess and deepen your comprehension of relational databases.
Let's dive straight into the first question:
Question 1:
Consider a database schema representing a library management system with the following tables:
- Books (book_id, title, author, genre, publication_year)
- Authors (author_id, author_name)
- Transactions (transaction_id, book_id, borrower_id, transaction_date, return_date)
- Borrowers (borrower_id, borrower_name, contact_info)
Write an SQL query to find the top 5 most borrowed books along with their titles and the total number of times each book has been borrowed.
Solution:
SELECT b.title AS book_title, COUNT(t.transaction_id) AS borrow_count
FROM Books b
JOIN Transactions t ON b.book_id = t.book_id
GROUP BY b.title
ORDER BY borrow_count DESC
LIMIT 5;
Explanation:
- We start by joining the Books table with the Transactions table based on the book_id.
- Using the COUNT() function along with GROUP BY, we count the number of transactions for each book.
- The result is sorted in descending order of borrow count and limited to the top 5 records.
Now, let's move on to the second question:
Question 2:
Consider a scenario where you have a table named Orders with the following structure:
- Orders (order_id, customer_id, order_date, total_amount)
Write an SQL query to calculate the average total amount spent by each customer, along with their customer_id and the number of orders they have placed. Exclude customers who haven't placed any orders.
Solution:
SELECT customer_id,
COUNT(order_id) AS order_count,
AVG(total_amount) AS avg_amount_spent
FROM Orders
GROUP BY customer_id
HAVING order_count > 0;
Explanation:
- We use the GROUP BY clause to group the orders by customer_id.
- The COUNT() function is used to calculate the number of orders placed by each customer.
- AVG() function computes the average total amount spent by each customer.
- The HAVING clause ensures that only customers with at least one order are included in the result set.
By dissecting these challenging SQL questions and their solutions, we aim to empower you to tackle complex database problems with confidence. Remember, practice is key to mastering SQL, and our platform provides ample resources and expert guidance to support your learning journey.
Whether you're seeking assistance with assignments or looking to expand your SQL skills, ProgrammingHomeworkHelp.com is your trusted companion in achieving database excellence. Stay tuned for more insightful content and expert solutions to propel your SQL proficiency to new heights.