title: Count id's or whatever on weeks in mysql
body: <p>I have a mysql table with a datetime field. Now, for statistics, I need to count how many entries are done in the weeks, 1st week, 2nd week, ...</p>
  
  <p>Weeks are from monday to sunday.</p>
  
  <p>For now, my idea is to calculate every monday in php and do a query. But 52 weeks do 52 querys.</p>
  
  <p>Is there perhaps another solution just in mysql?</p>
  
  <p>Thanks for your reply's</p>