How to combine 2 columns into a new one in sqlite

I have a table with 3 columns and I have to put the values from 2 columns into one in descending order.

+---+---+---+
| A | B | C |
+---+---+---+    
| z | 1 | 2 |  
| f | 5 | 7 | 
| s | 9 | 5 |
+---+---+---+

Using this example the output would be putting the values from column B and C into one like this:

+---+----+
| A | B  |
+---+----+ 
| s | 9  |
| f | 7  |
| f | 5  |
| s | 5  | 
| z | 2  |
| z | 1  |
+---+----+

How can I do this? Thanks.