title: Tableau check for multiple IDs across 2 groups
body: <p>I want to create a set in tableau, which will show either one of these two values: Y or N</p>
  
  <p>2 already existing columns are here important, "VAT-ID" and "CUSTOMER-ID". the new column should check if a customer-ID has multiple VAT-IDs. If yes, the value "Y" should be displayed, else "N".
  The table looks like: </p>
  
  <pre>
  customer-id  VAT-id       in-both
  123456       EE999999999  Y
  654321       AA999999999  N
  666666       GG999999999  N 
  123456       KK999999999  Y
  654321       AA999999999  N
  </pre>
  
  <p>any Help would be appreciated, I have tried <code>IF [CustomerID] = 1 AND Count([VAT-ID]) &gt; 1 THEN 'Y' ELSE 'N' END</code>  which didn't work.</p>