title: Columns Intersection
body: <p>Suppose i have a table like</p>
  
  <pre><code>ID     PROD     UNIT
  1    |  100  | X
  2   |  100   |  Y
  3   |  100   |  Z
  4   |  200   |  X
  5   |  200   |  Y
  6   |  300   |  Y
  7   |  300   |  Z
  </code></pre>
  
  <p>I want to obtain an intersection of values from UNIT column for each code from PROD column, by an SQL query. The number of products in table is variable but i need to intersect UNIT for all products.
  For my example, the result table would be a table with a single row, since all products from PROD have only one UNIT in common:</p>
  
  <pre><code>PROD    UNIT
  300     Y
  </code></pre>