SQL - Tricky Merging - sql

Question

I'm facing a tricky query to do. I hope your expertise will help me to sort it out.
There are 2 tables:
Table1 : Orders
Index ProductName OrderDate
0 a 03/03/1903
1 a 10/03/2014
2 b 01/01/2017
3 c 01/01/2019
Table2 : Product Specs
--> This table shows every change made in the Color of our products
Index ProductName Color ColorUpdatedOn
0 a Blue 01/01/1900
1 a Red 01/01/2014
2 a Yellow 01/01/2017
3 b Pink 01/01/2017
4 c Black 01/01/2018
5 c Black 31/12/2018
I would like to be able to retrieve all the data from Table1 with the Column Color et UpdatedOn
Index ProductName OrderDate Color ColorUpdatedOn
0 a 03/03/1903 Blue 01/01/1900
1 a 10/03/2014 Red 01/01/2014
2 a 01/01/2019 Yellow 01/01/2017
3 c 01/01/2019 Black 31/12/2018
Do you have any idea how I could do this ?
Thank you in advance for your help
Largo

Answer 1

Get the max() date of Product Specs table based on color,
then join it using year() function, applicable on mysql and mssql, not sure with other db.
select o.Index, o.ProdcutName, o.Date, t1.color, t1.ColorUpdatedOn
from Orders o
inner join
(select color, max(colorupdatedon) as ColorUpdatedOn
from productspecs
group by color) t1 on year(o.OrderDate) = year(t1.createdon)
but I would prefer using right() function since your year dates are at the end.
select o.Index, o.ProdcutName, o.Date, t1.color, t1.ColorUpdatedOn
from Orders o
inner join
(select color, max(colorupdatedon) as ColorUpdatedOn
from productspecs
group by color) t1 on right(o.OrderDate, 4) = right(t1.createdon, 4)

Answer 2

In a database that supports lateral joins (which is quite a few of them now), this is pretty easy:
select o.*, s.* -- select the columns you want
from orders o left join lateral
(select s.*
from specs s
where s.ProductName = o.ProductName and
s.ColorUpdatedOn <= o.OrderDate
order by s.ColorUpdatedOn desc
fetch first 1 row only
) s
on 1=1;
In SQL Server, this would use outer apply rather than left join lateral.
In other databases, I would use lead():
select o.*, s.* -- select the columns you want
from orders o left join
(select s.*,
lead(ColorUpdatedOn) over (partition by ProductName order by ColorUpdatedOn) as next_ColorUpdatedOn
from specs s
) s
on s.ProductName = o.ProductName and
o.OrderDate >= s.ColorUpdatedOn and
(o.OrderDate < s.next_ColorUpdatedOn or s.next_ColorUpdatedOn is null)

Answer 3

Assuming, the datatype for OrderDate and ColorUpdatedOn are both date, we can find the colors which was at the time of order.
For this I have used the anlytical/windowing function. The Hive query would look like this:
SELECT
y.ProductName, y.OrderDate, y.Color, y.ColorUpdatedOn
FROM (
SELECT
x.*,
DENSE_RANK() OVER(PARTITION BY x.ProductName, x.OrderDate ORDER BY x.recency ASC) AS relevance
FROM (
SELECT
a.*, b.color, b.ColorUpdatedOn, DATEDIFF(a.OrderDate, b.ColorUpdatedOn) AS recency
FROM
Order a
INNER JOIN
Product b
ON (
a.ProductName = b.ProductName
AND a.OrderDate >= b.ColorUpdatedOn
)
) x
) y
WHERE
y.relevance = 1;
The query could be made specific if you let me know the database you are using.
Let me know if it helps.