title: Oracle sql query sum data every month
body: <p>Let's say i have selected data from oktober until desember like this</p>
  
  <p><a href="https://i.stack.imgur.com/Vi5uR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Vi5uR.png" alt="enter image description here"></a></p>
  
  <p>i want to get sum of buying customer in every months (okt-des)
  The result i want is like table below</p>
  
  <p><a href="https://i.stack.imgur.com/HBAWx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HBAWx.png" alt="enter image description here"></a></p>
  
  <p>i already know how to get last day of months <br>but i don't have idea query in SQL to get result like i need</p>