Sometimes we need to fire trigger like after delete update some fields of another tables. for example if you have chat_message tables and when remove row on this table then we need to update "remove_counter(remove_counter + 1)" on users table. i did give you bellow example you can see how to write trigger code:
<pre class="prettyprint lang-php">
CREATE TRIGGER add_ban_counter_in_users
AFTER DELETE ON `chat_messages`
FOR EACH ROW
SET remove_counter = users.remove_counter + 1
WHERE users.id = old.user_id.....