Oracle SQL column tweak

How could I convert this

into this?

Answer

You can use coalesce() and a case expression:

select coalesce(col1, col2) as col3,
       (case when col1 is null then 'Add' else 'Remove' end) as col4
from t
where col1 is null or col2 is null;

EDIT:

You should fix your data model. Until then, you can cast() the values:

coalesce(cast(col1 as nvarchar2(255)), cast(col2 as nvarchar2(255))

You don’t really need to cast both values, but I don’t want to remember which column has which type.