• triggers can cancel a requested operation
• triggers can cause mutating table errors,
There are typically three triggering events that cause data triggers to 'fire':
• INSERT event (as a new record is being inserted into the database),
• UPDATE event (as a record is being changed),
• DELETE event (as a record is being deleted),
Structurally, triggers are either "row triggers" ( Row triggers define an action for every row of a table or "statement triggers"( statement triggers occur only once per INSERT, UPDATE, or DELETE statement,)
Furthermore, there are "BEFORE triggers" and "AFTER triggers" which run in addition to any changes already being made to the database,
Triggers do not accept parameters, but they do receive information in the form of implicit variables, For row- level triggers, these are generally OLD and NEW variables, each of which have fields corresponding to the columns of the affected table or view; for statement-level