title: Update a count (field) safely in SQL
body: <p>I want to implement SO like tags on userpost. I have a table called tag_data with columns tagId, title, count. I have a separate table that links the relationship between a post and the many tags it may use.</p>
  
  <p>Heres the problem, how do i get the current count, increase or decrease it by one and store it SAFELY. So no other connection/thread will update it between the time i do select and update?</p>