SELECT A.personid,
(SELECT Count(*) + 18618
FROM tbldemounbound AS B
WHERE B.personid < A.personid) AS Rank
INTO updateranks
FROM tbldemounbound AS A;
UPDATE tbldemounbound
INNER JOIN updateranks
ON tbldemounbound.personid = updateranks.personid
SET tbldemounbound.personid = [rank];