Updating Null values with non-nulls in SQL Server - sql

Question

I'm trying to go through a table and update currently null info if there is a previous entry that was not null. The code below is what I came up with but that's just updating every field so that every contact has the same fax number. Does someone who is smarter than me know what to do?
Thanks for the help.
UPDATE dbo.AAASTA_CONTACT
SET
CON_CSN = COALESCE(CRNT_RCD.CON_CSN, LST_RCD.CON_CSN),
CON_COMMENTS = COALESCE(CRNT_RCD.CON_COMMENTS, LST_RCD.CON_COMMENTS),
CON_EMAIL_ADDR = COALESCE(CRNT_RCD.CON_EMAIL_ADDR, LST_RCD.CON_EMAIL_ADDR),
CON_FAX_PH_NUM = COALESCE(CRNT_RCD.CON_FAX_PH_NUM, LST_RCD.CON_FAX_PH_NUM),
CON_HOME_PH_NUM = COALESCE(CRNT_RCD.CON_HOME_PH_NUM, LST_RCD.CON_HOME_PH_NUM),
CON_SEX_MF = COALESCE(CRNT_RCD.CON_SEX_MF, LST_RCD.CON_SEX_MF),
CON_PER_TITLE = COALESCE(CRNT_RCD.CON_PER_TITLE, LST_RCD.CON_PER_TITLE),
CON_WORK_PH_NUM = COALESCE(CRNT_RCD.CON_WORK_PH_NUM, LST_RCD.CON_WORK_PH_NUM),
CON_SUPPRESSMAILFL = COALESCE(CRNT_RCD.CON_SUPPRESSMAILFL, LST_RCD.CON_SUPPRESSMAILFL)
FROM
(
SELECT
CON.ALIAS_KEY,
CON.LAST_UPD,
CON.CON_CSN,
CON.CON_COMMENTS,
CON.CON_EMAIL_ADDR,
CON.CON_FAX_PH_NUM,
CON.CON_HOME_PH_NUM,
CON.CON_SEX_MF,
CON.CON_PER_TITLE,
CON.CON_WORK_PH_NUM,
CON.CON_SUPPRESSMAILFL,
RANK() OVER (PARTITION BY CON.ALIAS_KEY ORDER BY CON.LAST_UPD) AS UPD_RNK
FROM dbo.AAASTA_CONTACT CON
) CRNT_RCD
LEFT OUTER JOIN
(
SELECT
CON.ALIAS_KEY,
CON.LAST_UPD,
CON.CON_CSN,
CON.CON_COMMENTS,
CON.CON_EMAIL_ADDR,
CON.CON_FAX_PH_NUM,
CON.CON_HOME_PH_NUM,
CON.CON_SEX_MF,
CON.CON_PER_TITLE,
CON.CON_WORK_PH_NUM,
CON.CON_SUPPRESSMAILFL,
RANK() OVER (PARTITION BY CON.ALIAS_KEY ORDER BY CON.LAST_UPD) AS UPD_RNK
FROM dbo.AAASTA_CONTACT CON
) LST_RCD
ON CRNT_RCD.ALIAS_KEY = LST_RCD.ALIAS_KEY
WHERE CRNT_RCD.UPD_RNK=1
AND LST_RCD.UPD_RNK>1