Adding a Virtual Column

CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
                  ENAME VARCHAR2(10),
                  JOB VARCHAR2(9),
                  SAL NUMBER(7, 2),
                  DEPTNO NUMBER(2));
                  
ALTER TABLE emp
ADD (double_sal AS sal + sal);

DESCRIBE emp

INSERT INTO EMP VALUES (1, 'SMITH', 'CLERK',     800,    20);

SELECT * FROM emp;