title: In SQLite (or Postgres), can you have a table with a variable number of row elements?
body: <p>I am creating an activity table with many types of activities.  Let's
  say activities of type "jogging" will have elements a, b, and c  while
  activities of "football" will have elements a, d, and e.  Can I create a
  table in which the row elements for each column depend on that column's
  type?  I have considered creating one table for each activity type or
  creating a single table with rows for every activity's options, but
  there will be many activity types so it seems like a waste to use so
  many tables or leave so many rows blank.</p>