Question

Basically, I have a field in my table that shows when the latest activity was in a regular unix timestamp.

What I need is a way to count the rows that have had activity in the past 7 days.

Answer 1

select count(*)
  from someTable
 where lastActivity > UNIX_TIMESTAMP(NOW() - INTERVAL 7 day)

Note that this is 7 days worth of seconds.

If you want activity of last 7 calendar days

select count(*)
  from someTable
 where lastActivity > UNIX_TIMESTAMP(CURDATE() - INTERVAL 7 day)