In my dataset, I have two date columns, and showed as follow:

Year Month
1990 M1
1990 M2
1990 M3
1990 M4
1990 M5
1990 M6
1990 M7
1990 M8
1990 M9
1990 M10
1990 M11
1990 M12
1991 M1
1991 M2
..

May I ask:

How can I tell stata that my second column is a month,

And I want to merge them together to create a single date column

I would be grateful for any help you are able to provide.