Syntax:
DROP TRIGGER [IF EXISTS] [schema_name.]trigger_name

This statement drops a trigger. The schema (database) name is optional.
If the schema is omitted, the trigger is dropped from the default
schema. DROP TRIGGER was added in MySQL 5.0.2. Its use requires the
TRIGGER privilege for the table associated with the trigger. (This
statement requires the SUPER privilege prior to MySQL 5.1.6.)

Use IF EXISTS to prevent an error from occurring for a trigger that
does not exist. A NOTE is generated for a nonexistent trigger when
using IF EXISTS. See [HELP SHOW WARNINGS]. The IF EXISTS clause was
added in MySQL 5.1.14.

Triggers for a table are also dropped if you drop the table.

URL: http://dev.mysql.com/doc/refman/5.1/en/drop-trigger.html

