ORA-00001 : Unique Constraint Violated Caused by DATE VS Timestamp(6)

Create table tt1 (dt date primary key);Create table tt2(dt timestamp(6) primary key);Insert into tt2 values('25-NOV-13 04.18.47.138746000 PM');Insert into tt2 values('25-NOV-13 04.18.47.66 PM');commit;Insert into tt1 select * from tt2;

ORA-00001: unique constraint violated 
unique constraint (%s.%s) violated"

This is because Oracle does not store fractional part for DATE data type. These 2 rows are considered duplicate in TT1. This issue could happen in data migration project if you had not noticed the difference between date and timestamp(6) data type.