How to check values of different rows of a table - sql-server

Question

I have below sample input table. In real it has lots of records.
Input:
ID
Classification
123
1
123
2
123
3
123
4
657
1
657
3
657
4
For a 'ID', I want it's records should have 'Classification' column contains all the values 1, 2, 3 and 4. If any of these values are not present then that ID's records should be considered as an exception. The output should be as below.
ID
Classification
Flag
123
1
0
123
2
0
123
3
0
123
4
0
657
1
1
657
3
1
657
4
1
Can someone please help me with how can this can be achieved in sql server.
Thanks.

Answer 1

There are a couple of options here, which is more performant is up to you to test, not me (especially when I don't know what indexes you have). One uses conditional aggregation, to check that all the values are there, and the other uses a subquery and counts the DISTINCT values (as I don't know if there could be duplicate classifications):
SELECT *
INTO dbo.YourTable
FROM (VALUES(123,1),
(123,2),
(123,3),
(123,4),
(657,1),
(657,3),
(657,4))V(ID,Classification);
GO
CREATE CLUSTERED INDEX CI_YourIndex ON dbo.YourTable (ID,Classification);
GO
SELECT ID,
Classification,
CASE WHEN COUNT(CASE YT.Classification WHEN 1 THEN 1 END) OVER (PARTITION BY ID) > 0
AND COUNT(CASE YT.Classification WHEN 2 THEN 1 END) OVER (PARTITION BY ID) > 0
AND COUNT(CASE YT.Classification WHEN 3 THEN 1 END) OVER (PARTITION BY ID) > 0
AND COUNT(CASE YT.Classification WHEN 4 THEN 1 END) OVER (PARTITION BY ID) > 0 THEN 1 ELSE 0
END AS Flag
FROM dbo.YourTable YT;
GO
SELECT ID,
Classification,
CASE (SELECT COUNT(DISTINCT sq.Classification)
FROM dbo.YourTable sq
WHERE sq.ID = YT.ID
AND sq.Classification IN (1,2,3,4)) WHEN 4 THEN 1 ELSE 0
END AS Flag
FROM dbo.YourTable YT;
GO
DROP TABLE dbo.YourTable;