alter table exchange partition

Hello, I am trying to execute a alter table exchange partition and of course I am getting: ora-14097: column type mismatch I created the partitioned table using a simple create table statement.I am created the table that I want to exchange with the partition as a CTAS. I am able to cast most of my select results as my destination datatypes but I am stuck on a timestamp. If I select from user_tab_columns the 2 columns show like select DATA_TYPE,DATA_LENGTH,DATA_PRECISION,DATA_SCALE,NULLABLE,COLUMN_ID from user_tab_columns TIMESTAMP(6) 11 6 N 9 TIMESTAMP(6) 20 6 N 9 How can I specify the data length of