SQL> DESC employees
 Name                                      Null?    Type
 ----------------------------------------- -------- -----------------
 EMPLOYEE_ID                               NOT NULL NUMBER(6)
 FIRST_NAME                                         VARCHAR2(20)
 LAST_NAME                                 NOT NULL VARCHAR2(25)
 EMAIL                                     NOT NULL VARCHAR2(25)
 PHONE_NUMBER                                       VARCHAR2(20)
 HIRE_DATE                                 NOT NULL DATE
 JOB_ID                                    NOT NULL VARCHAR2(10)
 SALARY                                             NUMBER(8,2)
 COMMISSION_PCT                                     NUMBER(2,2)
 MANAGER_ID                                         NUMBER(6)
 DEPARTMENT_ID                                      NUMBER(4)

SQL> begin
  2   execute immediate 'CREATE TABLE EMPLOYEES(ID NUMBER)';
  3  end;
  4  /
begin
*
ERROR at line 1:
ORA-00955: name is already used by an existing object
ORA-06512: at line 2


SQL> DECLARE
  2    E_TAB_EXISTS EXCEPTION;
  3    PRAGMA EXCEPTION_INIT(E_TAB_EXISTS,-955);
  4  BEGIN
  5    execute immediate 'CREATE TABLE EMPLOYEES(ID NUMBER)';
  6  EXCEPTION
  7   WHEN E_TAB_EXISTS THEN
  8     dbms_output.put_line('Table already exists');
  9  end;
 10  /
Table already exists

PL/SQL procedure successfully completed.

SQL> ed
Wrote file afiedt.buf

  1  DECLARE
  2    CURSOR c_tab
  3        IS
  4    SELECT table_name
  5      FROM user_tables
  6     WHERE table_name = 'EMPLOYEES';
  7    v_tab VARCHAR2(30);
  8  BEGIN
  9    OPEN  c_tab;
 10    FETCH c_tab INTO v_tab;
 11    IF c_tab%NOTFOUND THEN
 12      execute immediate 'CREATE TABLE EMPLOYEES(ID NUMBER)';
 13    ELSE
 14      dbms_output.put_line('Table already exists, not created.');
 15    END IF;
 16    CLOSE c_tab;
 17* END;
SQL> /
Table already exists, not created.

PL/SQL procedure successfully completed.

SQL>