oh sorry for that In webi you can go for if statement.
Like
if state(Merged Object) inlist(Put all the states which are part of East Coast like 'California') then "East Coast"
elsif state(Merged Object) inlist(Put all the states which are part of central Zone) then "Central Zone"
elsif state(Merged Object) inlist(Put all the states which are part of west zone) then "west zone"
elsif state(Merged Object) inlist(Put all the states which are part of mountain zone) then "Mountain Zone" else 'NA'
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for merging please make sure that al the state objects from each tables should have same data type.