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Triggers and exceptions
Exceptions raised by triggers have a statement severity; they roll
back the statement that caused the trigger to fire.
This rule applies to nested triggers (triggers that are fired by other
triggers). If a trigger action raises an exception (and it is not caught),
the transaction on the current connection is rolled back to the point before
the triggering event. For example, suppose Trigger A causes Trigger B to fire.
If Trigger B throws an exception, the current connection is rolled back to
the point before the statement in Trigger A that caused Trigger B to fire.
Trigger A is then free to catch the exception thrown by Trigger B and continue
with its work. If Trigger A does not throw an exception, the statement that
caused Trigger A, as well as any work done in Trigger A, continues until the
transaction in the current connection is either committed or rolled back.
However, if Trigger A does not catch the exception from Trigger B, it is as
if Trigger A had thrown the exception. In that case, the statement that caused
Trigger A to fire is rolled back, along with any work done by both of the
triggers.
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