The name of the column or columns that make up the index key.

    You can create a multisegmented index key by naming two or more
    columns, which are joined to form the index key. All the columns
    must be part of the same table. Separate multiple column names
    with commas.

                                   NOTE

       If column-name refers to a column defined as CHAR, VARCHAR
       or LONG VARCHAR data type, the size of the column must be
       less than or equal to 254 characters, or the SIZE IS clause
       must be used.