title: Oracle SQL Constraint where clause
body: <p>I have the table Tester on oracle with the following columns:</p>
  
  <ul>
  <li>TesterID</li>
  <li>TesterName</li>
  <li>IsDefault</li>
  <li>Application_ID</li>
  </ul>
  
  <p>TesterID is the primary key. 
  Now I want that there can only be one Default Tester, which means only one Tester can have the calues IsDefault =Y at an ApplicationID.</p>
  
  <p>I tried it with a constraint:</p>
  
  <pre><code>alter table Tester add constraint Tester_ISDEFAULT UNIQUE(IsDefault,Application_ID);
  </code></pre>
  
  <p>Is it possible to make the unique key on where isdefault= Y?</p>
  
  <p>Thanks for help!</p>