title: Looking for SQL constraint: SELECT COUNT(*) from tBoss < 2
body: <p>I'd like to limit the entries in a table. Let's say in table <em>tBoss</em>. Is there a SQL constraint that checks how many tuples are currently in the table? Like</p>
  <pre><code>SELECT COUNT(*) from tBoss &lt; 2
  </code></pre>
  <p>Firebird says:</p>
  <blockquote>
  <p>Invalid token.
  Dynamic SQL Error.
  SQL error code = -104.
  Token unknown - line 3, column 8.
  SELECT.</p>
  </blockquote>