title: Is there a difference between "not null" and "not null enable"?
body: <p>When we define a table in Oracle we may define the columns as:</p>
  
  <pre><code>"NAME" VARCHAR2(80) NOT NULL ENABLE
  </code></pre>
  
  <p>My question is I could not understand the meaning of "ENABLE" in this statement. What would be the difference if we just define as  <code>"NAME" VARCHAR2(80) NOT NULL</code> ?</p>