title: How to discover in a trigger whether the NULL value was passed to a nullable column?
body: <p>How can one figure out in a BEFORE INSERT Trigger, whether the user has passed the NULL - value for an null-able column  <strong>explicit</strong>, or whether the user hasn't pass any value at all for that column.</p>
  
  <p>In other words, I will be able to do following:</p>
  
  <pre><code>create table t (id, NUMBER, str VARCHAR2(30) );
  
  create Trigger trg 
  befor INSERT on t
  FOR earch row
  DECLARE
  BEGIN
  IF :NEW.str is NULL
  THEN
    IF &lt;NULL-Value was explicit passed&gt; THEN
      dbms_output.put_line( 'user has passed NULL');
    ELSE 
      dbms_output.put_line( 'user has passed nothing');
    END IF;
  END IF;
  END;
  /
  </code></pre>
  
  <p>and then after</p>
  
  <pre><code>INSERT INTO t (id, str) VALUES (1, NULL);
  </code></pre>
  
  <p>I will see</p>
  
  <pre><code>&gt; user has passed NULL
  </code></pre>
  
  <p>and after </p>
  
  <pre><code>INSERT INTO t (id) VALUES (1);
  </code></pre>
  
  <p>I will see</p>
  
  <pre><code>&gt; user has passed nothing
  </code></pre>