title: Database column with default constraint
body: <p>I am creating a database column like this:</p>
  
  <pre><code>Alter table tablename
  add column columnname null
  add constraint df_columnname default 0
  </code></pre>
  
  <p>After executing above SQL, the new column is added to table with null values. </p>
  
  <p>Does the <code>constraint df_cloumnname</code> have no meaning here?</p>
  
  <p>Please clarify on this..</p>