title: How to use oracle check constraints to limit number of registration?
body: <p>I've a user table with unique user_id. User can register using there id. Now I want to limit the max. registration per user using CHECK constraints. so I use this:</p>
  
  <pre><code>.... CHECK(select count(user_id) from user where ... ...)
  </code></pre>
  
  <p>But it's show subquery cannot use in check constraints.</p>
  
  <p>Can anyone tell me how can I add this condition?</p>