title: `delete()` vs. `fetch()` with underspecified relative restrictions
body: <p>My database has a number of sessions.</p>
  <pre class="lang-py prettyprint-override"><code>@schema
  class Session(dj.Manual):
      definition = &quot;&quot;&quot;
      -&gt; Subject
      session_datetime: datetime
      &quot;&quot;&quot;
  </code></pre>
  <p>I could fetch or delete them as follows.</p>
  <pre class="lang-py prettyprint-override"><code>total_sessions = session.Session # N=4
  total_sessions.fetch()   # Successful output
  total_session.delete()   # Successful cascading delete prompt
  </code></pre>
  <p>If I'm only interested in sessions after a given year/month, I can generate a query with a relative restriction, fully specifying <code>datetime</code>.</p>
  <pre class="lang-py prettyprint-override"><code>later_sessions1 = (session.Session &amp; 'session_datetime &gt; &quot;2021-06-01 12:00:00&quot;') # N=2
  later_sessions1.fetch()   # Successful output
  later_sessions1.delete()  # Successful cascading delete prompt 
  </code></pre>
  <p>If I don't fully specify <code>datetime</code>, I can still fetch the data, but deletion fails.</p>
  <pre class="lang-py prettyprint-override"><code>later_sessions2 = (session.Session &amp; 'session_datetime &gt; &quot;2021-06&quot;') # N=2
  later_sessions2.fetch()   # Successful output
  later_sessions2.delete()  # OperationalError: (1292, &quot;Incorrect datetime value: '2021-06' for column 'session_datetime' at row 1&quot;)
  </code></pre>
  <p>Is this intended? Should <code>fetch()</code> and <code>delete()</code> fail under the same conditions?</p>
  <hr />
  <p>EDIT: calling <code>make_sql()</code> on <code>later_sessions2</code> returns the following</p>
  <pre><code>'SELECT DISTINCT `subject`,`session_datetime` FROM `test_session`.`session` WHERE(session_datetime &gt; &quot;2021-06&quot;)'
  </code></pre>
  <p>If called on the fully specified <code>later_sessions1</code>, the last <code>WHERE</code> component includes the full datetime.</p>