Agent limits the history in 2 measures - overall and per job.

The number 100k you've mentioned - is it overall number?
If yes - what is the limit...

SELECT 1 WHERE EXISTS (
SELECT 1 FROM View1 WHERE field1 = 'Y'
union all
SELECT 1 FROM View2 WHERE field1 = 'Y'
)

It does exactly what I think it does.

It makes sure that there is no way to get an...

This will be different:

select t1.col1, t1.col2,t2.col1.t2.col2 
from (select col1,col2 from table1 group by col1,col2)t1
join (select col1,col2 from table2 group by col1,col2) t2
on t1.column1=t2.column1 

AND NOT EXISTS (SELECT * FROM Tbl3 WHERE Tbl3.ID=c.ID )

How many records per SKU?
Is it a unique key?
Is the uniqueness enforced through the UNIQUE constraint?

Apart from that - the logic of the query seems troubled.

I cannot see SKU mentioned anywhere begore.

What is the correlation between SKU and PKey?

Here is hardcode SQL for you:
SELECT SL.{Required Columns}
FROM ServerList SL
INNER JOIN (
SELECT [Server],[DB's], MIN(Ranking) as MinRanking, MAX(Ranking) as MaxRanking
FROM [YourTable]
GROUP BY  [Server],[DB's]
)...