Types of Triggers
The various types of triggers are as follows:
1) Row Triggers: A row trigger is fired each time the
table is the triggering statement. For example, if an UPDATE statement updates
multiple rows of a table, a row trigger is fired Once for row affected by the
UPDATE statement. If the triggering affects no rows, the trigger is not
executed at all. Row trigger used when the trigger action code depends on the
data provided triggering, statement or rows that are affected.
For example, if the trigger is keeping the track of
all the affected records.
2) Statement Triggers: A row trigger is fired once on
behalf of the triggering statement, independent of the number of rows the
statement affects (even if no rows are affected). Statement useful if the code
in the trigger action does not depend on the provided by the triggering
statement or the rows affected.
For example, if the trigger makes the security check
on the time or the
3) Before and After Triggers: When defining a trigger
one can the trigger timing, i.e. to specify when the triggering action is to
executed in relation to the triggering statement. Before and After to both row
and the statement triggers.
The two of them are described as follows:
i) Before Triggers: BEFORE triggers execute the
trigger action before the triggering statement.
These types of triggers are commonly used in the following
situation:
a) BEFORE triggers are used when
the trigger action should determine whether or not the triggering statement
should be allowed to complete. By using a BEFORE trigger, you can eliminate
unnecessary processing of the triggering triggers.
b) Before Statement are used to derive specific column values before
completing a triggering INSERT or UPDATE statement.
ii) After Triggers: AFTER trigger executes the
trigger action after the triggering statement is executed. These types of
triggers are commonly used in the following situation:
a) AFTER triggers are used when
you want the triggering statement to complete before executing the trigger
action.
b) If a BEFORE trigger is already
present, an AFTER trigger can perform different actions on the same triggering
Statement.
4) INSTEAD OF
Triggers: The INSTEAD OF triggers are the written specially for
modifying views, which cannot be directly modified through SQL DMIL,
statements. As you know that a view virtual table that draws its data from some
underlying base INSTEAD OF triggers, the UPDATE, ELETE INSERT can be directly
performed on the underlying tables.
The INSTEAD OF triggers provide a transparent way of
modifying views that cannot be modified directly through SQL DML statements.
