title: Oracle: Conditional not-null constraint when both conditions are true
body: <p>I have to alter a table to create a conditional not null constraint on a specific column so that it cannot be null if col1 and col2 have values. </p>
  
  <p>First, what is a conditional not null constraint? </p>
  
  <p>Second, can you please provide a syntax on how to accomplish such thing? </p>