title: how to write a trigger to insert and update unique varchar field.....?
body: <p>I have a table named <code>contact</code>:</p>
  
  <pre><code>Create table contact (
      Contact_ID int PK NOT NULL,
      Name varchar(20),
      MMS_Contact_ID varchar(10) NOT NULL
  )
  </code></pre>
  
  <p>When am inserting the first 2 rows, <code>Contact_ID</code> and <code>Name</code>, i want to automatically update the third row (<code>MMS_Contact_ID</code>). Like this:</p>
  
  <pre><code>contact_ID    Name     MMS_Contact_ID
  --------------------------------------           
  1               A        MMSC000001
  </code></pre>
  
  <p>When am inserting the second record (id = 2 and Name = B), how can 
  <code>MMS_Contact_ID</code> automatically be updated to MMSC000002?</p>
  
  <p>I think a trigger can help me with this, but how?</p>