SQL if column1 matches column2 add 1 to column3

I am currently working on SQL.

If the data in column1 matches column2 then 1 should be added an index in column3.

E.G.

1. column1 column2
2. B7 A8
3. A8 Q9
4. L1 X2

So It must search through both columns and add 1 to a third column