How to obtain unique values from a set of columns for each row in a table.
Consider the following table structure:

COL1 | COL2 | COL3 | COL4
--------------------------
  1  |  1   |  2   |  3
  2  |  2   |  2   |  4
  4  |  5   |  6   |  7

The desired result should look like this:

COL1 | COL2 | COL3 | COL4
--------------------------
  1  |  2   |  3   | NULL
  2  |  4   | NULL | NULL
  4  |  5   |  6   |  7

I was able to achieve this by case statements by comparing each columns with each other. Are there any other way to do this?