Question

How do I obtain the highest value for each year within a table. So let’s say we have a table movies and I want to find the highest profiting film for each year.

This is my attempt so far:

SELECT year, MAX(income - cost) AS profit, title
FROM Movies m, Movies m2
GROUP BY year

I am pretty certain it is going to need some sub selects but I can’t visualise what I need to do. I was also thinking probably some sort of distinct option to rule out duplicate years.

Title  Year   Income  Cost  Length
A      2000   10      2     2
B      2000   9       7     2

So from this the expected result would be

Title  Year   Profit
A      2000   8

Answer 1

I’m guessing slightly at what you want, but since you’ve not specified any RDBMS a generic solution would be:

SELECT  m.Year, (m.Income - m.Cost) AS Profit, m.Title
FROM    Movies m
        INNER JOIN
        (   SELECT  m.Year, MAX(m.Income - m.Cost) AS Profit
            FROM    Movies
            GROUP BY m.Year
        ) MaxProfit
            ON MaxProfit.Year = m.Year
            AND MaxProfit.Profit = (m.Income - m.Cost)
ORDER BY m.Year

You can also do this using analytic functions if your DBMS permits. e.g. SQL-Server

WITH MovieCTE AS
(   SELECT  m.Year,
            Profit = (m.Income - m.Cost), 
            m.Title,
            RowNumber = ROW_NUMBER() OVER(PARTITION BY m.Year ORDER BY (m.Income - m.Cost) DESC)
    FROM    Movies
)
SELECT  year, Profit, Title
FROM    MovieCTE
WHERE   RowNumber = 1

It is possible I have misunderstood your exact criteria, but I am sure the same priciples can be applied, you will just need to alter the grouping and the join in the first example, or the partition by in the second.