title: Sql Conditional Not Null Constraint
body: <p><br>
  I am curious to know is it possible to create a conditional not null constraint in sql? In otherwords is it possible to create a constraint such that a column B can be null as long column A contains lets say 'NEW' but if the contents of column A changes to something else then column B is no longer allowed to be null? <br>
  And to extend on that, it is then possible to make it so that column B must be null or empty as long as column A says 'NEW'?<br>
  Thanks All :D <br></p>