Apply a flag before Append between 2 table

Hi Team,

I have 2 fact tables. I need to append both tables  with the common date_key field to connect date_key field of calender.

Before append i need to add a column in both table like Flag ='A' in 1st table and  Flag ='B'  in 2nd table.

This 'A' value  will add in each column of 1st table.

Same 'B' value  will add in each column of 2nd table.

After that i want to append both table.

whenever a new value will come in  1st table than value 'A' will be automatically added in 1st table.

Same way with 2nd table when new  value will come in  2nd table then B will automatically added in 2nd table.

As you know we have append earlier then the vale added in appended table automatically.

Please let me know how can i add a Flag that will automatically get value A whenever new value come in that table.

Thanks,

Narender