INDEXES can be unique or non–unique. Unique indexes guarantee that no two rows of a table have duplicate VALUES in the columns that define the index. Non–unique indexes do not impose this restriction on the column values.

Oracle RECOMMENDS that you do not explicitly define unique indexes on TABLES; uniqueness is strictly a logical concept and should be associated with the definition of a table. Alternatively, define UNIQUE integrity constraints on the desired columns. Oracle enforces UNIQUE integrity constraints by automatically defining a unique index on the unique key

Indexes can be unique or non–unique. Unique indexes guarantee that no two rows of a table have duplicate values in the columns that define the index. Non–unique indexes do not impose this restriction on the column values.

Oracle recommends that you do not explicitly define unique indexes on tables; uniqueness is strictly a logical concept and should be associated with the definition of a table. Alternatively, define UNIQUE integrity constraints on the desired columns. Oracle enforces UNIQUE integrity constraints by automatically defining a unique index on the unique key