dbadmin@mutation_mutation > create table t1 ( a number, b long);

Table created.

-- insert some data in t1
-- i have not inserted any

dbadmin@mutation_mutation > create table t2 (a number, b long);

Table created.
dbadmin@mutation_mutation > copy from dbadmin/passCode@mutation to dbadmin/passCode@mutation append t2 using select * from t1;

Array fetch/bind size is 15. (arraysize is 15)
Will commit when done. (copycommit is 0)
Maximum long size is 80. (long is 80)
   0 rows selected from dbadmin@mutation.
   0 rows inserted into T2.
   0 rows committed into T2 at dbadmin@mutation.

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there is hard bound limitation in this method..i dont have that on top of my head~.
if this is not working, you have to use exp / imp