Query to pull data from column based off max value of second column - sql

Question

I have a table that has [Order], [Yield], [Scrap], [OpAc] columns. I need to pull the yield based on the max value of [OpAc].
Order
Yield
Scrap
OpAc
1234
140
0
10
1234
140
0
20
1234
130
10
30
1234
130
0
40
1234
125
5
50
1234
110
15
60
1235
140
0
10
1235
138
2
20
1235
138
0
30
1235
138
0
40
1235
138
0
50
1235
137
1
60
1235
137
0
70
Expected Results
Order
Yield
1234
110
1235
137
The query that I have tried is
select [Order], [Yield], MAX([OpAc]) as Max_OpAc
from SCRAP
GROUP BY [Order], [Yield]
order by [order]
This produces
Order
Yield
Max_OpAc
1234
110
60
1234
125
50
1234
130
40
1234
140
20
1235
137
70
1235
138
50
1235
140
10
I've tried setting up some CTE queries to break it down into separate functions but I keep getting caught at this step.
WITH CTE1 AS(
SELECT ROW_NUMBER() OVER(PARTITION BY [Order] ORDER BY [Order],[OpAc]) AS RN , *
FROM SAP_SCRAP
),
This proved to be redundant due to the fact that the [OpAc] field is sequential for each step.
Thanks in advance for any help

Answer 1

You almost got it!
WITH Orders_By_OpAc_Desc AS (
SELECT
[Order],
[Yield].
ROW_NUMBER() OVER (PARTITION BY [Order] ORDER BY OpAc DESC) AS [rn],
FROM
SCRAP
)
SELECT [Order],
[Yield]
FROM
Orders_By_OpAc_Desc
WHERE
rn = 1
The trick here is ROW_NUMBER() OVER (PARTITION BY [Order] ORDER BY OpAc DESC) AS [rn]. It might be confusing to understand in SQL, but when expressed in words it's a bit clearer.
This statement takes each group of rows with the same Order value (PARTITION BY [Order]), orders each group by OpAc in descending order so that the higher OpAc values end up "on top" of the group (ORDER BY OpAc DESC), and numbers each row in the group "top" to "bottom", starting with 1 (ROW_NUMBER()).
Meaning, each row with this number set to 1 has the highest OpAc value for the OrderId.
Wrap that into a CTE and then select just the rows with this number (rn) set to 1. Voi-la.

Answer 2

You definitely want the OVER (PARTITION BY) but MAX() is also an option here. You want something like:
SELECT
*
FROM
(
SELECT
t3.*
, MAX(OpAc) OVER (PARTITION BY [Order]) max1
FROM
SCRAP t3
) a
WHERE
a.Max1 = a.OpAc
for MAX()
Depending on your SQL Server edition, version, and query needs, you may be able to use FIRST_VALUE() as well:
SELECT
DISTINCT
t3.[Order],
FIRST_VALUE(Yield) OVER(PARTITION BY [Order] ORDER BY OpAc DESC) Yield
FROM
SCRAP t3

Answer 3

You were so close. Just missing an ORDER BY OpAc DESC in your ROW_NUMBER function.
SQL Fiddle
MS SQL Server 2017 Schema Setup:
CREATE TABLE orders (
[Order] int null
, Yield int null
, Scrap int null
, OpAc int null
);
INSERT INTO orders ([Order], Yield, Scrap, OpAc)
VALUES (1234,140,0,10)
, (1234,140,0,20)
, (1234,130,10,30)
, (1234,130,0,40)
, (1234,125,5,50)
, (1234,110,15,60)
, (1235,140,0,10)
, (1235,138,2,20)
, (1235,138,0,30)
, (1235,138,0,40)
, (1235,138,0,50)
, (1235,137,1,60)
, (1235,137,0,70)
;
Query 1:
WITH CTE1 AS (
SELECT *
, ROW_NUMBER() OVER(PARTITION BY [Order] ORDER BY OpAc DESC) as row_num
FROM orders
)
SELECT *
FROM CTE1 as c
WHERE c.row_num = 1
Results:
| Order | Yield | Scrap | OpAc | row_num |
|-------|-------|-------|------|---------|
| 1234 | 110 | 15 | 60 | 1 |
| 1235 | 137 | 0 | 70 | 1 |