Have done some more testing. From what I see, MySQL's FROM_UNIXTIME() function does not support negative epoch timestamps (just as the inverse function UNIX_TIMESTAMP() does not either).
It looks like I could use the DATE_ADD function
SELECT Name, DATE_ADD('1970-01-01', INTERVAL Date_of_birth second) As DOB FROM Test
gives me 1964-08-11 00:00:00 which is correct.
What I need now is a way to format this date the way we use it in Norway which is 11.08.1964 or dd.mm.yyyy
It still have to be done inside the query. Could it be done ?