title: How can I Update column value to Old value plus New value from other table using Trigger?
body: <p>How can I Update column value to Old value plus New value from other table using Trigger if that value has already have an entry?
  What I wanted is something like the following. Notice the bold and italicized part.</p>
  
  <pre><code>DELIMITER$$
  CREATE TRIGGER trigger_name AFTER INSERT
  ON table_one FOR EACH ROW
  BEGIN
    INSERT INTO table_two(clmn_id, clmn_one) VALUES(NEW.clmn_id_fk,NEW.clmn_a)
    ON DUPLICATE KEY UPDATE clmn_one = VALUES(<b><i>clmn_one + NEW.clmn_a</b></i>);
  END$$
  DELIMITER;</code></pre>