title: Firebird query selecting previous row
body: <p>who can help me with my query?</p>
  
  <p>here's the screenshot of the table.</p>
  
  <p><img src="https://i.stack.imgur.com/UMc6a.png" alt="enter image description here"></p>
  
  <p>i want to compute the range/minutes between two dates.
  My idea is to subtract the second row of FORMATTED_DATEMODIFIED to first row of FORMATTED_DATEMODIFIED and so on. i want to subtract the date from previous row.</p>
  
  <p>anyone can help? thank you very much!!</p>