That's a little different. I thought you said random "values", not "strings". Of course, you could convert the following to strings.
--===== Create the list of the first 1,000,000 integers
-- and establish a random sort order for usage.
-- The ISNULL''s are to make the columns NOT NULL
SELECT SortOrder = IDENTITY(INT,1,1)
,UniqueRandomValue = ISNULL(t.N,0)
,IsUsed = ISNULL(0,0)
FROM dbo.fnTally(1,1000000) t
ORDER BY NEWID()