thank you for your help eval
but now i am converting the obsolete mysql to mysqli (which is such a pain to me), so i guess the php code would be like?
IFNULL(column1,column2) AS finalcolumn
ps: i use if "IFNULL" because i want the criteria to be: if column1 is not null then use column1, otherwise use column2, which always contain a value
also, is there any websites that i can learn mysqli command? i found that php.net is sometimes intimidating