DB Projects Help >> Introduction to Triggers
How Triggers Are Used
Causes complement the normal features of Oracle to offer a very custom made collection control system. For example, a set off can control DML businesses against a desk to those supplied during common enterprise hours. You can also use triggers to:
Automatically produce made line values
Prevent incorrect transactions
Enforce complicated security authorizations
Enforce referential reliability across nodes in a dispersed database
Enforce complicated enterprise rules
Provide obvious occurrence logging
Provide auditing
Maintain synchronous desk replicates
Gather information on desk access
Modify desk information when DML phrases are supplied against views
Publish information about collection activities, person activities, and SQL phrases to following applications
Parts of a Trigger
A set off has three primary parts:
A leading to occurrence or statement
A leading to occurrence or report is the SQL report, collection occurrence, or person occurrence that causes a set off to fireplace. A leading to occurrence can be one or more of the following:
An INSERT, UPDATE, or DELETE report on a particular desk (or perspective, in some cases)
A CREATE, ALTER, or DROP report on any schema object
A collection beginning or example shutdown
Particular problem information or any problem message
A person logon or logoff
A set off restriction
A set off stops describes a Boolean concept that must be real for the set off to fireplace. The set off actions is not run if the set off stops assess to fake or unfamiliar. In the example, the set off stops is:
new.parts_on_hand < new.reorder_point
Consequently, the set off does not fireplace unless the variety of available areas is less than a provide reorder quantity.
A set off action
A set off actions is the method (PL/SQL prevent, Coffee application, or C callout) that contains the SQL phrases and value to be run when the following activities occur:
A leading to report is supplied.
The set off stops assess to real.
Like saved processes, a set off actions can:
Contain SQL, PL/SQL, or Coffee statements
Define PL/SQL expressions constructs such as issues, always the same, cursors, and exceptions
Define Coffee expressions constructs
Call saved procedures
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