Ordered Value by Column / Row

Question

Its a little difficult to explain. It might be easier to skip to the examples.

A table has an id and four columns that each allow null.

ID, Col1, Co         


        

Answer 1

select value from (    
    select col1 as value from table_name where col1 is not null
     union
    select col2 as value from table_name where col2 is not null
     union
    select col3 as value from table_name where col3 is not null
     union
    select col4 as value from table_name where col4 is not null     
) order by value