SELECT Row_NUMBER() OVER (ORDER BY <your criteria>) as RowIndex, other fields
FROM MyTable
Обновление
Чтобы добавить это как поле, вы можете сделать:
UPDATE T
SET T.Indexfield = X.RowIndex
FROM MyTable T
INNER JOIN (SELECT Row_NUMBER() OVER (ORDER BY <your criteria>) as RowIndex, other fields
FROM MyTable) as X
ON X.<field> = T.<Field>