I would hope that SQL itself would change it to an INNER JOIN when applicable, but it certainly won't hurt to try -- or verify using the query plan that...

Check to see if the db A on each instance allows cross-database ownership chaining:

SELECT is_db_chaining_on, *
FROM sys.databases
WHERE name IN ('A')

If it's 1, then security...

We would have to see the tables definition and the query itself to give you a reliable answer here.

Yes, eventually it will get compressed automatically.  Although SQL doesn't actually do any page compression until the page gets full.

Just plain DATEDIFF(DAY, ...) will do that.  By definition, DATEDIFF counts the number of times the midnight boundary is reached/crossed between two dates/datetimes.

DECLARE @CurrentYearStart INT
DECLARE @CurrentYearEnd INT
SET @CurrentYearStart = 201801
SET @CurrentYearEnd = 201805

SELECT *
FROM @test-2 t_curr
INNER JOIN @test-2 t_prev
...

To fix the immediate problem, try running:

DBCC CHECKIDENT ('dbo.CmEvent', RESEED, 55845910)

Better yet, rid yourself of the foolish and damaging myth that all tables should be clustered...

As with any nonclus index, SQL estimating that too many pages will be needed from the nonclus index causes SQL to drop back to just scanning the main table.  I...

For the CCI, SQL will effectively have to scan all the rows for every query.  If you can a nonclus index, SQL may be able to just do lookups to...