I'm looking to pull information from a SQL database and have let the user select 4 different options to show only the rows related to them.

The table has two columns all based on dates (a start date and a finished date)
The user can choose to view only the startdate, only the enddate, the dates that haven't finnished (are NULL),or all the dates.

What command can i put in to my SQL search statement to find a field that has content in/not in?