title: Creating Unique Key in MySQL table referring to date
body: <p>Question on preventing duplicated entry in my simple web form.</p>
  
  <p>My table record user input from a web form, and distinguished by date e.g. DATE(). How to prevent user with the same name to enter information twice in a single date, e.g. same username cannot be entered twice in the same date, but can be entered at other date?</p>