title: how to create trigger to do concatenation of fields
body: <p>I have 1 table like this:</p>
  
  <pre><code>user
  ----------------------------------------
  id | first_name | last_name | full_name
  ----------------------------------------
  </code></pre>
  
  <p>I want to write a trigger which will concat the first_name and last_name to full_name.</p>
  
  <p>I have tried below trigger :</p>
  
  <pre><code>delimiter |
  create trigger fullname after insert on user
  for each row
  begin
  update user set full_name=(select concat(first_name,last_name) from user where id=new.id)where id=new.id;
  end;
  |
  </code></pre>
  
  <p>It's shows this error while inserting data to user table:</p>
  
  <p><code>#1442 - Can't update table 'user' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.</code></p>