Months_Between/Add_Months/Last_Day

Select ename,

  round(Months_Between(Sysdate,Hiredate))

from employee;

  

Select Ename,Hiredate,

  Add_Months(Hiredate,6),

  Add_Months(Hiredate,-6)

from employee;

Select 

  Sysdate,

  Next_Day(Sysdate,1) -- 1~7 (月～日)

from dual;

Select 

  Hiredate,

  Last_Day(Hiredate)

From employee;