title: Can you help me when I select Desc in dropdown list google sheet I want the value become unique number
body: <p>I have a google Spreadsheet.</p>
  <ul>
  <li>Column A = Unique number,</li>
  <li>Column B = Desc</li>
  </ul>
  <p>In column C, I use data validation from column B. I want when I select 1 value the result in column C should be column A. I tried include image to become more clear. Do you have any ideas?</p>
  <p>Thank you.</p>
  <p><a href="https://i.stack.imgur.com/o40K4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/o40K4.png" alt="https://i.stack.imgur.com/o40K4.png" /></a></p>