If you have an existing table and want to know how many columns are in the table and how they are defined, you can use the system view USER_TAB_COLUMNS as shown in the following tutorial exercise:

SQL> COL data_type FORMAT A12;

SQL> SELECT column_name, data_type, data_length

FROM user_tab_columns WHERE table_name = 'EMPLOYEES';

COLUMN_NAME    DATA_TYPE DATA_LENGTH

------------------------------ ------------ -----------

EMPLOYEE_ID    NUMBER   22

FIRST_NAME    VARCHAR2   20

LAST_NAME    VARCHAR2   25

EMAIL     VARCHAR2   25

PHONE_NUMBER    VARCHAR2   20

HIRE_DATE    DATE    7

JOB_ID     VARCHAR2   10

SALARY     NUMBER   22

COMMISSION_PCT    NUMBER   22

MANAGER_ID    NUMBER   22

DEPARTMENT_ID   NUMBER   22