Selecting top most row in Bigquery based on conditions - sql

Question

I have a huge table, where sometimes 1 product ID has multiple specifications. I want to select the newest but unfortunately, I don't have the date information. please consider this example dataset
Row ID Type Sn Sn_Ind
1 3 SLN SL20 20
2 1 SL SL 0
3 2 SL SL 0
4 1 M SL21 10
5 3 M SL21 10
6 1 SLN SL20 20
I used the below query to somehow group the products in give them row numbers like
with cleanedMasterData as(
SELECT *
FROM (
SELECT *,ROW_NUMBER() OVER(PARTITION BY ID ORDER BY Sn DESC, Sn_Ind DESC) AS rn
FROM `project.dataset.table`
)
-- where rn = 1
)
select * from cleanedMasterData
Please find below the example table after cleaning
Row ID Type Sn Sn_Ind rn
1 1 SL SL 0 1
2 1 M SL21 10 2
3 1 SLN SL20 20 3
4 2 SL SL 0 1
5 3 M SL21 10 1
6 3 SLN SL20 20 2
but if you see for ID 2 and 3, I can easily select the top row with where rn = 1
but for ID 1, my preferred row would be 2 because that is the newest.
My question here is how do I prioritise a value in column so that I can get the desired solution like :
Row ID Type Sn Sn_Ind rn
1 1 M SL21 10 1
2 2 SL SL 0 1
3 3 M SL21 10 1
As the values are fixed in Sn column - for ex SL, SL20, SL19, SL21 etc - If somehow I can give weightage to these values and create a new temp column with weightage and sort based on it, then?
Thank you for your support in advance!!

Answer 1

Consider below
SELECT *
FROM `project.dataset.table`
WHERE TRUE
QUALIFY ROW_NUMBER() OVER(PARTITION BY ID ORDER BY IF(Sn = 'SL', 0, 1) DESC, Sn DESC) = 1
If applied to sample data in your question - output is

Answer 2

It wasn't difficult, I tried a few things and it worked out. If anyone can optimize the below solution even more that would be awesome.
first the dataset
#standardSQL
WITH `project.dataset.table` AS (
SELECT 1 ID, 'SLN' Type, 'SL20' Sn, 20 Sn_Ind UNION ALL
SELECT 1 , 'SL' , 'SL' , 0 UNION ALL
SELECT 2 , 'SL' , 'SL' , 0 UNION ALL
SELECT 1 , 'M' , 'SL21' , 10 UNION ALL
SELECT 3 , 'M' , 'SL21' , 10 UNION ALL
SELECT 1 , 'SLN' , 'SL20' , 20
)
with weightage as(
SELECT
*,
MAX(CASE Sn WHEN 'SL' THEN 0 ELSE 1 END) OVER (PARTITION BY Sn) AS weightt,
FROM
`project.dataset.table`
ORDER BY
weightt DESC, Sn DESC
), main as (
select * EXCEPT(rn, weightt)
from (
select * ,ROW_NUMBER() OVER(PARTITION BY ID ORDER BY weightt DESC, Sn DESC) AS rn
from weightage )
where rn = 1
)
select * from main
after this, I can get the desired result
Row ID Type Sn Sn_Ind
1 1 M SL21 10
2 2 SL SL 0
3 3 M SL21 10