title: Checking if specific tuple exists in table
body: <p>Is there a way to check if a specific tuple exists in a table in a where-in statement?</p>
  
  <p>Something like:</p>
  
  <pre><code>create table Test(A int, B int);
  
  insert into Test values (3, 9);
  insert into Test values (6, 7);
  insert into Test values (7, 6);
  insert into Test values (3, 4);
  
  select A, B
  from Test
  where (B, A) in Test;
  </code></pre>
  
  <p>Expected output:</p>
  
  <pre><code>6|7
  7|6
  </code></pre>