If you don't need your data ordered by FootnoteField
, you can go with GoatCo answer.
But if you do then:
with cte as (
select
FootnoteText, FootnoteField,
min([FootnoteField]) over(partition by FootnoteText) as min_FootnoteText
from Table1
)
select
FootnoteText, FootnoteField,
dense_rank() over(order by min_FootnoteText)
from cte