I got the problem is when I run following command in Oracle, I encounter the error.
Truncate table mytable;
ORA-02266: unique/primary keys in table referenced by enabled foreign keys
You have to swap the TRUNCATE statement to DELETE statements, slower and logged but that's the way to do it when constraints are in place.
Either that or you can find the foreign keys that are referencing the table in question and disable them temporarily.
select 'ALTER TABLE '||TABLE_NAME||' DISABLE CONSTRAINTS '||CONSTRAINT_NAME||';' from user_constraints where R_CONSTRAINT_NAME='<pk-of-table>';
pk-of-table is the name of the primary key of the table being truncated
Run the output of the above query. When done, remember to enable them again, just change
DISABLE CONSTRAINTS to