Calculated field in MySQL

Hello, I got the following error message from MySQL: --- Query failed. MySQL said: Unknown column 'AGE' in 'where clause' query = SELECT *, (Year(Now()) - Year(BDAY)) + ((DAYOFYEAR(Now())-DAYOFYEAR(BDAY))/365) as AGE FROM Katalog WHERE AGE >= 31 AND AGE <= 50 AND IS_MEM_EXP = 0 AND IS_OPEN = 1 ORDER BY INPUT_DATE DESC --- Now, obviously the column should exist, since I am creating it in the query, but I do not seem to be able to find the bug. If I would have used Access, I would have created a query inside the database from my table and SELECT from that, but since I am not I have to find other ways. What I would like to do the most, would be to create a field in the table, which would calculate the field inside the database, but it does not seem to be possible, though it would save me a lot of trouble every time I need that column in my application. Could someone either tell me whats wrong with my query or tell me what I need to do to make such a calculated field. Much appreciated. Morten Twellmann