How to find all (group-based) rows containing MIN/MAX values for a particular column in SQL Server? - sql

Question

I have temporary table (#TempPackages) which looks like this:
EntryId (PK) PackageId SubProductID SubProductSequence
1 1111 17 3
2 1111 28 4
3 1111 33 1
4 1111 67 5
5 1111 122 2
6 2222 18 4
7 2222 29 5
8 2222 33 9
9 2222 103 7
10 2222 99 11
11 3333 256 5
12 3333 333 6
13 3333 789 3
14 3333 1023 2
15 3333 9845 1
I need a query which will give me the rows with the minimum/maximum SubProductSequence value for each unique PackageId. For the table above, the query would return this:
EntryId (PK) PackageId SubProductID SubProductSequence
3 1111 33 1
4 1111 67 5
6 2222 18 4
10 2222 99 11
12 3333 333 6
15 3333 9845 1
The EntryId column was something that I added while trying to solve this, as it gives me a unique column to join the same table on to (to ensure I still only end up with 15 rows in my joined table).
I tried this - just to get the MIN():
SELECT
*
FROM
#TempPackages p1
INNER JOIN
#TempPackages p2 ON p1.EntryId = p2.EntryId
AND p1.SubProductSequence = (
SELECT
MIN(SubProductSequence)
FROM
#DeparturesToUpdate)
Obviously this is wrong, because the INNER JOIN is superfluous and the SELECT MIN() clause is wrong as it selects the rows with the minimum overall sequence numbers, not the minimum sequence numbers per package.
Any suggestions about the best way to do this?

Answer 1

One way is to use the ROW_NUMBER() function:
SELECT
EntryId
, PackageId
, SubProductID
, SubProductSequence
FROM
( SELECT
EntryId
, PackageId
, SubProductID
, SubProductSequence
, ROW_NUMBER() OVER (PARTITION BY PackageId
ORDER BY SubProductSequence ASC)
AS rna
, ROW_NUMBER() OVER (PARTITION BY PackageId
ORDER BY SubProductSequence DESC)
AS rnd
FROM
#TempPackages
) AS tmp
WHERE
rna = 1
OR rnd = 1 ;
ROW_NUMBER() is a ranking function that is used with OVER clause. What it basically does in this case, is it groups the rows with same PackageId (that is done with the PARTITION BY PackageId), then orders them by SubProductSequence (ascending or descending) and assigns a row_number, starting from 1 for each packageId.
So, the subquery would return this, if it was run alone:
EntryId (PK) PackageId SubProductID SubProductSequence rna rnd
3 1111 33 1 1 5
5 1111 122 2 2 4
1 1111 17 3 3 3
2 1111 28 4 4 2
4 1111 67 5 5 1
6 2222 18 4 1 5
7 2222 29 5 2 4
9 2222 103 7 3 3
8 2222 33 9 4 2
10 2222 99 11 5 1
15 3333 9845 1 1 5
14 3333 1023 2 2 4
13 3333 789 3 3 3
11 3333 256 5 4 2
12 3333 333 6 5 1
The WHERE condition added in the external query is obvious afterwards.

Answer 2

Improving on Bohemian's idea -
;WITH MinMax AS
(SELECT PackageId ,
MIN(SubProductSequence) [Min],
MAX(SubProductSequence) [Max]
FROM #TempPackages
GROUP BY PackageId )
SELECT EntryId, SubProductSequence, TP.PackageId, SubProductID FROM #TempPkges TP
INNER JOIN MinMax MM ON TP.PackageId = MM.PackageId
AND (SubProductSequence = MM.[Min] OR SubProductSequence = MM.[Max])
And then, you can add your own ORDER BY

Answer 3

WITH t1 AS
(SELECT PackageId,MIN(SubProductSequence) minm,MAX(SubProductSequence) maxm
FROM ##TempPackages
GROUPBY PackageId
)
SELECT pk.EntryId, pk.PackageId,pk.SubProductID, pk.SubProductSequence
FROM ##TempPackages pk INNER JOIN t1
ON pk.PackageId = t1.PackageId
WHERE pk.SubProductSequence = t1.minm OR
pk.SubProductSequence = t1.maxm