title: Multi keys in SQL WHERE IN clause
body: <p>Say you have <code>Accounts</code> table where <code>ID</code> column is PK and <code>TaxID+AccountNumber</code> is unique constraint:</p>
  
  <pre><code>select * from Accounts where ID in (100, 101)
  </code></pre>
  
  <p>now you want to make similar query using the natural key:</p>
  
  <pre><code>select * from Accounts 
  where {TaxID, AccountNumber} in 
    ({"0123456", "2000897"}, {"0125556", "2000866"})
  </code></pre>
  
  <p>So this involves tuples and looks pretty legitimate. Is it possible to express somehow with ANSI SQL? Maybe in some specific SQL extension? If not, why (will appreciate any speculations)?</p>