在mysql中找到最大数量

Question

How do I find the most popular book among all customers from the table above? (cid = 'customer id')?

I have

select Title, sum(c.quantity) from cart c group by c.ISBN;

which gives me the following results

+-----------------------------------------+-----------------+ | Title | sum(c.quantity) | +-----------------------------------------+-----------------+ | Writing Skills | 5 | | Fundamentals of Database Systems | 2 | | Database Management Systems | 5 | | Data Mining, Practical Machine Learning | 4 | +-----------------------------------------+-----------------+

I know the Max() function in mysql can achieve my goal, but I do not know to implement Max() and Sum() together.

Thanks!

Answer 1

To get most popular book/books you can use following query

select c.ISBN,c.Title, sum(c.quantity) soldQuantity
from cart c 
group by c.ISBN,c.Title
having soldQuantity = (
    select sum(quantity)
    from cart  
    group by ISBN,Title
    order by sum(quantity) desc 
    limit 1
)

Note there can be more than 1 books which share same highest quantity

Answer 2

The following SQL statement should give you the book with the most quantity

SELECT
    Title, 
    sum(c.quantity) AS total_count
FROM 
    cart c 
GROUP BY 
    c.ISBN 
ORDER BY 
    total_count DESC
LIMIT 1

Note: You really should put the books in a seperate table titled "books" with two columns, "id" and "title". You can then change the "title" column in your original table to "book_id" and make it a foreign key to books.id. This will greatly improve the speed of your SQL calls.

Hope this helps!

Answer 3

Hi one approach would be using sub queries like this:

SELECT TITLE, MAX (SUMMATION)
FROM (SELECT TITLE, SUM (C.QUANTITY) SUMMATION
      FROM CART C
      GROUP BY TITLE, C.ISBN) LIST
GROUP BY TITLE, SUMMATION