title: SQL Constraint : only one record per day for a particular key
body: <p>There is a way to create a constraint or something where I can have only one record for a Day for a FK column? I.E.</p>
  
  <pre><code>PK(IDENTITY(1,1))  FK_FIELD DATETIME
  ------------------------------
  1                  1        2012-02-22 4:50 p.m.
  2                  2        2012-02-23 12:00 p.m.
  3                  2        2012-02-23 9:00 p.m.  -- This one should not be allowed because the FK_Field 2 would have 2 record in one day.
  4                  1        2012-02-23 08:00 a.m 
  </code></pre>
  
  <p>Hopefully someone understand what im trying to archieve.</p>
  
  <p>Thanks in advance.</p>