The name of a domain created in a CREATE DOMAIN statement. SQL
    gives the column the data type specified in the domain. For more
    information on domains, see the CREATE DOMAIN statement.

    For most purposes, you should specify a domain instead of an
    explicit data type.

    o  Domains ensure that all columns in multiple tables that serve
       the same purpose have the same data type. For example, several
       tables in the sample personnel database refer to the domain
       ID_DOM.

    o  A domain lets you change the data type for all columns that
       refer to it in one operation by changing the domain itself
       with an ALTER DOMAIN statement.

       For example, if you want to change the data type for the
       column EMPLOYEE_ID from CHAR(5) to CHAR(6), you need only
       alter the data type for the domain ID_DOM. You do not have to
       alter the data type for the column EMPLOYEE_ID in the tables
       DEGREES, EMPLOYEES, JOB_HISTORY, or SALARY_HISTORY, nor do you
       have to alter the column MANAGER_ID in the DEPARTMENTS table.

    However, you might not want to use domains when you create tables
    if:

    o  Your application must be compatible with Oracle RDBMS.

    o  You are creating intermediate result tables that do not need
       the advantages of domains.