Database Administrator’s Guide. Contents. Previous Next. Page of Search. This Book This Release. Table of Contents. open Oracle Database. Overview of Triggers. A trigger is a named program unit that is stored in the database and fired (executed) in response to a specified event. The specified event. Prerequisites. The trigger must be in your own schema or you must have ALTER ANY TRIGGER system privilege. In addition, to alter a trigger on DATABASE.
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Automatically generate derived column values Enforce referential integrity across nodes in a distributed database Enforce complex business rules Provide transparent event logging Provide auditing Maintain synchronous table replicates Gather statistics on table access Modify table data when DML statements are issued against views Publish information about database events, user events, and SQL statements to subscribing applications Restrict DML operations against a table to those issued during regular business hours Enforce security authorizations Prevent invalid transactions Caution: By default, a trigger is automatically enabled when it is created; however, it can later be disabled.
However, unless autonomous transactions are used, any audit information generated by a trigger is rolled back if the triggering statement is rolled back.
Depending on the type of triggering statement, certain correlation names might not have any meaning.
It cannot transfer control to another section. Also, if global package variables are updated within a trigger, then it is best to initialize those variables in a BEFORE statement trigger.
Oracle / PLSQL: AFTER INSERT Trigger
Returns the grantees of a grant event in the OUT parameter; returns the number of grantees in the return value. Only committed triggers are fired. Do not define triggers that duplicate database features. Oracle Database Oeacle for a description of the various types of triggers and Oracle Database Application Developer’s Guide – Fundamentals for more information on how to design triggers.
Complex Security Authorizations and Triggers Triggers are commonly used to enforce complex security authorizations for table data. This way, the trigger can minimize its overhead when the column of interest is not being changed. If a triggering statement omits a column list, the trigger fires when any column of the associated table is updated.
For example, to enable the disabled trigger named Reorderenter the following statement:. Although you can use both triggers and integrity constraints to define and enforce any type of integrity rule, Oracle strongly recommends that you use triggers to constrain data input only in the dsparadores situations:.
Views are an disoaradores mechanism to provide logical windows over table data. Although triggers can be written to record information similar to that recorded by the AUDIT statement, triggers should be used disparadorws when more detailed audit information is required.
The statements in the trigger body operate under the privilege domain of the trigger owner, not the privilege domain of the user issuing the triggering statement. Given a position 1 for top of stackit returns the error message at that position on error stack.
When an event is published, certain run-time context and attributes, as specified in the parameter list, are passed to the callout subprogram. Debugging Triggers You can debug a trigger using the same facilities available for stored subprograms.
Do not define triggers that duplicate features already built into Oracle Database. A compound trigger can fire at more than one timing point. The specified event is associated with either a table, a view, a schema, or the database, and it is one of the following:.
This implementation requires care for multiple-row updates.
Before, after, each row and table level triggers [Oracle]
This condition must contain correlation names and cannot contain a query. By default, a trigger is created in enabled state. The following statement, inside a trigger, returns the owner of the trigger, not the name of user who is updating the table:.
This allows most foreign key constraint actions to be implemented xisparadores their obvious after-row trigger, providing the constraint is not self-referential.
These statements are executed if the triggering statement is entered and if the trigger restriction if any evaluates to TRUE. This section provides an example of each of these trigger applications. For example, use triggers to provide value-based auditing for each row. That is the only problem with this technique for foreign key updates.
A loop-back database link makes a local table appear remote by defining an Oracle Net path back to the database that contains the link.
Enabling and Disabling Triggers
For example, the following statement shows the dependencies for the triggers in the HR schema: The relationship of the data orafle p and f is lost.
The parent row corresponding to this nested table element can be accessed using the parent qualifier. It is when the triggering statement affects many rows that a compound trigger has a performance benefit. With AFTER row triggers, affected data blocks must be read logical read, not physical read once for the trigger and then again for the triggering statement.
Database Events Database events are related to entire instances or schemas, not individual tables or rows. Returns the list of object owners of objects being modified in the event. The order in which Oracle Database fires these triggers is indeterminate.
When the database is opened for the first time after a role change. You can choose what combination of operations should fire the trigger. However, when the view query gets complex, the system implicitly cannot translate the DML on the view into those on the underlying tables.
You can create triggers on index-organized tables. NEW values but not the: To ensure that multiple triggered actions occur in a specific order, you must consolidate these actions into a single trigger for example, by having the trigger call a series of procedures. Only system-defined database events can be detected this way.
In more realistic examples, you might test if one column value is less than another. Session and Execution time Auditing. The declarative constraint features provided with the database offer oraccle following advantages when compared to constraints defined by triggers:.
An updatable view is one that lets you perform DML on the underlying table.