title: How to show null values for a field based on a constraint
body: <p>I seem to be having a hard time with creating a psql check script to choose whether or not to display a column of data for my row.  I have a birthday column as date and a gender column as text.  A constraint(s) needs to be created on the birthday field where the gender column would display null values for people on the list under the age of 18 and those who are over the age of 18, their gender shown.  Thank you!</p>