The format is:

          [CONSTRAINT table_constraint_name]
            UNIQUE (unique_columns)

The UNIQUE can be defined as a column constraint:

          CREATE TABLE      EMPLOYEE_TBL (
                 ...
                 BADGE_ID   CHAR(4)   NOT NULL UNIQUE,
                 ...        );

The UNIQUE can be defined as a named table constraint:

          CREATE TABLE EMPLOYEE_TBL (
                 ...
                 BADGE_ID   CHAR(4)   NOT NULL,
                 ...
                 CONSTRAINT EMPLOYEE_UNQ1
                     UNIQUE (BADGE_ID),
                 ... );

                                               or

          CREATE TABLE      SAMPLE_TBL (
                 SAMPLE1    CHAR(4)   NOT NULL,
                 SAMPLE2    CHAR(4)   NOT NULL,
                 ...
                 CONSTRAINT SAMPLE_UNQ2
                     UNIQUE (SAMPLE1, SAMPLE2)
                 ... );