Simplify in sql [duplicate] - mysql

Question

This question already has answers here:
SQL select only rows with max value on a column [duplicate]
(27 answers)
Closed 1 year ago.
I have some task that I should do it with sql.
Below is the function I currently use.
(SELECT ProductName, sum(Quantity*Price) Revenue, Country
FROM products p
JOIN orderdetails d
ON p.ProductID = d.ProductID
JOIN orders o
ON o.OrderID = d.OrderID
JOIN customers c
ON c.CustomerID = o.CustomerID
WHERE Country =
(
SELECT DISTINCT Country
FROM customers
LIMIT 1
)
GROUP BY ProductName
ORDER BY Revenue DESC
LIMIT 1)
UNION
(SELECT ProductName, sum(Quantity*Price) Revenue, Country
FROM products p
JOIN orderdetails d
ON p.ProductID = d.ProductID
JOIN orders o
ON o.OrderID = d.OrderID
JOIN customers c
ON c.CustomerID = o.CustomerID
WHERE Country =
(
SELECT DISTINCT Country
FROM customers
LIMIT 1,1
)
GROUP BY ProductName
ORDER BY Revenue DESC
LIMIT 1)
UNION
(SELECT ProductName, sum(Quantity*Price) Revenue, Country
FROM products p
JOIN orderdetails d
ON p.ProductID = d.ProductID
JOIN orders o
ON o.OrderID = d.OrderID
JOIN customers c
ON c.CustomerID = o.CustomerID
WHERE Country =
(
SELECT DISTINCT Country
FROM customers
LIMIT 2,1
)
GROUP BY ProductName
ORDER BY Revenue DESC
LIMIT 1)
My task is "Find best selling products based on revenue for each country!"
The result I want is below:
ProductName
Revenue
Country
Tofu
279
Argentina
Côte de Blaye
18445
Austria
You can access the data I use from this link RawDatabase
the sample data that I use is like this
ProdName
Country
Revenue
coco
Argentina
120
bread
Austria
10000
crunch
Austria
13265
Cote de Blaye
Austria
18445
milk
Argentina
254
Tofu
Argentina
279
From this data I want to select only the best product for each country by revenue. In the data there were 21 country. What should I do so I can get the result below
ProductName
Revenue
Country
Tofu
279
Argentina
Côte de Blaye
18445
Austria
The only way in my mind is only filtering the data by each country then get the best product then union all of them like the code I give on top. I wonder if there's another way.

Answer 1

Using row_number window function or compare to country maxrevenue
DROP TABLe if exists t;
create table t
(ProdName varchar(20), Country varchar(20), Revenue int);
insert into t values
('coco' ,'Argentina' ,120),
('bread' ,'Austria' ,10000),
('crunch','Austria' ,13265),
('Cote de Blaye' ,'Austria', 18445),
('milk' ,'Argentina' ,254),
('Tofu' ,'Argentina' ,279);
select *
from
(
select prodname,country,revenue,
row_number() over(partition by country order by revenue desc) rn
from t
) s
where rn = 1;
or
select *
from t
join (select t.country,max(t.revenue) maxrevenue from t group by t.country) t1
on t1.country = t.country and t1.maxrevenue = t.revenue;
+---------------+-----------+---------+----+
| prodname | country | revenue | rn |
+---------------+-----------+---------+----+
| Tofu | Argentina | 279 | 1 |
| Cote de Blaye | Austria | 18445 | 1 |
+---------------+-----------+---------+----+
2 rows in set (0.001 sec)