SQL & PL/SQL

Hi,
I have two tables Encounter & Encounter_History. They have same columns. One column is of type CLOB. My requirement is to retrieve all the distinct records from both the tables with order by a date column. But problem is, UNION does not work in case of CLOB data type.

I know it will work if I use UNION ALL, but it returns duplicate records.

Please give me suggestion, how to solve this problem.

For example: The following query does not work since column1 is a CLOB data type

select column1 from table1
union
select column1 from table2

Thanks