Combining three tables with two dynamic values - mysql

Question

I'm trying to create a database for a guessing game where a player should guess the value of a given product. I have three tables;
One table for the products with the following columns:
ProductID
ProductName (VarChar)
One table for the players with the following columns
PlayerID
PlayerName (VarChar)
One table where the players, the products and their guesses are stored, i.e
GuessID
PlayerID
ProductID
Guess (Int)
I'm an trying to find a way to combine which player (PlayerName) that made the highest guess (Guess) for EVERY product (ProductName), i.e a way to summarize every single product, the highest guess for each product and the name och player who made the guess.
So far, I have only been able to get the correct ProductName and the correct Guess-value for each product. Somehow this doesn't work for PlayerName and i keep getting the wrong Name each time.
SELECT pl.PlayerName, MAX(g.Guess), p.ProductName
FROM
guess g
INNER JOIN player pl on g.PlayerID = pl.PlayerID
INNER JOIN product p on g.ProductID = p.ProductID
GROUP BY g.ProductID;
I guess my problem is that each row related to a specific product holds two dynamic values; Guess and PlayerID which is giving me problems whenever i try to sort by Max(Guess). I can't make any sense of the PlayerID that is chosen for the query stated above. It doesn't make any sense to me.
I would appreciate if any of you guys could point me in the right direction.
Cheers.

Answer 1

Use a correlated subquery to select the highest guess for each product, then select the related players and products records in the outer query, like :
SELECT
p.productname, u.playername, g.guess as "max guess"
FROM
guess_table g
INNER JOIN product_table p ON p.productid = g.productid
INNER JOIN players_table u on u.playerid = g.playerid
WHERE g.guess = (SELECT MAX(guess) FROM guess_table WHERE productid = p.productid)

Answer 2

You can make use of last value in this query. You can also use first value by ordering desc (you don't have to give unbounded preceding and following. Also, this is based on assumption that guess is unique within product name, so that ordering will be consistent.
Sample data and output would have helped to see if it is expected or not but I think it will work here based on what you have mentioned.
SELECT distinct p.ProductName,
last_value(Guess) over (partition by p.ProductName order by Guess rows between
unbounded preceding and unbounded following ) GuessNumber,
last_value(pl.PlayerName) over (partition by p.ProductName order by Guess rows
between unbounded preceding and unbounded following ) PlayerName
FROM guess g
inner join player pl on g.PlayerID = pl.PlayerID
inner join product p on g.ProductID = p.ProductID

Answer 3

One method is to use something of a hack in MySQL:
SELECT SUBSTRING_INDEX(GROUP_CONCAT(pl.PlayerName ORDER BY g.guess DESC), ',', 1) as PlayerName,
MAX(g.Guess), p.ProductName
FROM guess g JOIN
player pl
ON g.PlayerID = pl.PlayerID JOIN
product p
ON g.ProductID = p.ProductID
GROUP BY p.ProductName;
This method definitely has limits. The internal string representation for GROUP_CONCAT() is limited to about 1000 characters (although that can be expanded). The above assumes that the names do not contain commas (although other separators can be used).
The better solution is to use window functions, but these are available only in MySQL 8+.