Determine the name of the column with a null value nearest the last column

I have five columns in a mysql table

-id

-field_1

-field_2

-field_3

-field_4

-field_5

Field_5 is the last column of the table i have named transactions. If i have a select statement like

select * from transactions where id = 4,how would i know the name of the column nearest the column field_5 that is null.