Can the values of index fields in a database table be duplicated, or must they be unique?

Index field values in a database table can be duplicated if the index is not unique.

• A regular (non-unique) index speeds up searches but allows duplicate values.
• A unique index guarantees that the values in the indexed column or set of columns will not be duplicated.

For example, an index on the "age" field may not be unique, as many users can have the same age. An index on the "email" field is usually made unique to prevent duplication.