how to update existing date and insert new date in php MYSQL

hello i have little problem in updating date

my first table is

DONOR
 donor-nic----username-----status
 111----------ali----------available
 222---------usman--------notavailable
 

my second table is

DONATION
 donation_id------donor_nic-----date---
 1----------------111----------2012/03/04
 2---------------111-----------2012/06/07
 3----------------111---------2012/07/08
 4----------------222---------2012/03/03
 

now i am editing profile like
change date: 2012/07/07
change status: available/not available

i want to do that.. if donor that is editing profile/status.. select the date that already exists in donation table with his donor_nic then it will update his date..
if donor select new date that does not exist in donation table then it will insert this date..

anyone plz help me.. i dunt knw how to select all the dates of donor (111)
and then match this date from the new date.. plzz helpp mee

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