mysql sum from one of two columns
 

How do you get the sum from two columns, selecting only one column at a time by whichever number is smaller?

For example, you have this:
col1, col2
2, 1
1, 2
2, 1

When you do the select sum query, it replies: "3".

it's like this:

SELECT SUM( IF( col1 < col2, col1, col2 ) ) AS small_sum FROM table;