Guarantee a Unique Index

A unique index ensures that no two rows have the same index value, including NULL. The system checks for duplicate values when the index is created, if data already exists, and checks each time data is added or modified with an insert or update.

You can easily enforce uniqueness—using the unique keyword—on global indexes because they are not partitioned. Local indexes are partitioned; enforcing uniqueness requires additional constraints.

To enforce uniqueness on local indexes, the partition keys must:
For example, you can impose uniqueness in these instances:

You cannot enforce uniqueness on round-robin partitioned tables with local indexes.

Related concepts
Create Indexes on Tables