Hi,
Here you goes.
1.) Create first projection and insert your table.
2.) Create one more projection and insert your table and put filter text = 'GW3'.
3.) Join both of them as 'left outer' join.
4.) In join node, create one more claculated column as 'date_alt1'
and give condition as ..
if(isnull("date_alt"),'NULL',"date_alt")
5.) Join it with your upper projection.
Br
Sumeet

