title: MySQL - How to measure the amount of space used by certain rows?
body: <p>I am working on a project management program, built on a LAMP stack.  I have tentatively chosen not to provide each one of my clients with their own database, but rather to combine all business' data into one large database.</p>
  
  <p>The first column in all database tables is business_id.  This row indicates which business a certain piece of data belongs to, which keeps us from exposing Business 1's data to Business 2.</p>
  
  <p>But as I try to iron out the billing kinks, it would be very useful to be able to run a cron job once a month to determine how much database space each business is using.  So here's my question: Is there a way to get MySQL to return the number of bytes used by all rows WHERE business_id = 'x'?</p>