Get value based on date - sql

Question

I am trying to get the price point of a product based on future pricing. I can't really do it by Max (Expiration Date) since the price points are different. And I also can't do a Max(Price) since the high price might be the one expiring or it could be the new one. My data would look like this:
Supplier
Product
Price
Effective Date
Expiration Date
Supplier 1
A
800
04-01-2121
12-31-2023
Supplier 1
A
1000
01-01-2121
03-31-2023
Supplier 1
B
500
04-01-2121
12-31-2023
Supplier 1
B
400
01-01-2121
03-31-2023
Supplier 2
D
200
01-01-2121
12-31-2023
Supplier 2
C
600
01-01-2121
12-31-2023
The result I am trying to get is below:
Supplier
Product
Price
Effective Date
Expiration Date
Supplier 1
A
800
04-01-2121
12-31-2023
Supplier 1
B
500
04-01-2121
12-31-2023
Supplier 2
D
200
01-01-2121
12-31-2023
Supplier 2
C
600
01-01-2121
12-31-2023
Any ideas?

Answer 1

To have the product information when expirationdate is the greatest we can product wise group the rows in descending order of expirationdate and find the row with lowest serial number for each product or we can simply use subquery to select the information where expirationdate=max(expirationdate) within the product group.
First approach will be more efficient. But if your dbms doesn't support row_number() then you can use second approach.
Schema:
create table mydata(Supplier varchar(30),Product varchar(30), Price int,EffectiveDate date, ExpirationDate date);
insert into mydata values('Supplier 1', 'A', 800 ,'04-01-2121', '12-31-2023');
insert into mydata values('Supplier 1', 'A', 1000 ,'01-01-2121', '03-31-2023');
insert into mydata values('Supplier 1', 'B', 500 ,'04-01-2121', '12-31-2023');
insert into mydata values('Supplier 1', 'B', 400 ,'01-01-2121', '03-31-2023');
insert into mydata values('Supplier 2', 'D', 200 ,'01-01-2121', '12-31-2023');
insert into mydata values('Supplier 2', 'C', 600 ,'01-01-2121', '12-31-2023');
Query#1
WITH cte
AS (SELECT supplier,
product,
price,
effectivedate,
expirationdate,
ROW_NUMBER ()
OVER (PARTITION BY product
ORDER BY expirationdate DESC)
rn
FROM mydata)
SELECT supplier,
product,
price,
effectivedate,
expirationdate
FROM cte
WHERE rn = 1
Output:
supplier
product
price
effectivedate
expirationdate
Supplier 1
A
800
2121-04-01
2023-12-31
Supplier 1
B
500
2121-04-01
2023-12-31
Supplier 2
C
600
2121-01-01
2023-12-31
Supplier 2
D
200
2121-01-01
2023-12-31
Query#2 for older version of DBMS:
SELECT supplier,
product,
price,
effectivedate,
expirationdate
FROM mydata m
where effectivedate =
(select max(effectivedate) from mydata md where m.product=md.product)
Output:
supplier
product
price
effectivedate
expirationdate
Supplier 2
D
200
2121-01-01
2023-12-31
Supplier 2
C
600
2121-01-01
2023-12-31
Supplier 1
B
500
2121-04-01
2023-12-31
Supplier 1
A
800
2121-04-01
2023-12-31
db<>fiddle here

Answer 2

It looks you can accomplish what you need with a simple row_number by numbering the rows decending ordered against your ExpirationDate and filtering for the first row in each group.
select Supplier, Product, Price, EffectiveDate, ExpirationDate from (
select Supplier, Product, Price, EffectiveDate, ExpirationDate, row_number() over (partition by Product order by ExpirationDate desc)Seq
from table
)t
where Seq=1