title: MySQl - update field by counting data in other table
body: <p>There are two tables. One is users info "users", one is comments info "comments".</p>
  
  <p>I need to create new field "comments" in users table, that contains number of comments of that user. Table "comments" has "user" field with user's id of that comment.</p>
  
  <p>What is optimal way to count number of comments by every user so far?</p>
  
  <p>With php you should write script that selects every user and than count number of his comments and then update "comments" field. It is not hard for me, but boring.</p>
  
  <p>Is it possible to do it without php, only in MySQL?</p>