title: When does a query/subquery return a NULL and when no value at all?
body: <ol>
  <li><p>If a query/subquery doesn’t find any matching rows, then it either returns NULL or no value at all, thus not even a NULL value. Based on
  what criteria does a query/subquery return a NULL and when doesn’t it return any results, not even a NULL value?</p></li>
  <li><p>Will a scalar subquery always return NULL, when no
  matching rows are found? I assume most-outer scalar query also returns
  NULL if no rows are found?</p></li>
  <li><pre><code>SELECT FirstName, LastName, YEAR(BirthDate)
  FROM Persons
  WHERE YEAR(BirthDate) IN (SELECT YearReleased FROM Albums);
  </code></pre>
  
  <ul>
  <li><p>If the subquery finds no results, is the WHERE clause of the outer
  query translated into <code>WHERE YEAR(BirthDate) IN (null);</code>?</p></li>
  <li><p>If WHERE clause is translated into <code>WHERE YEAR(BirthDate) IN();</code> instead, shouldn’t that be an error condition, since how can <code>YEAR(BirthDate)</code> value be compared to nothing?</p></li>
  </ul></li>
  </ol>