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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Joins, with some exceptions, as documented in Oracle Database Administrator’s Guide. This trigger is an AFTER statement trigger, so it is fired after an unsuccessful statement execution, such as unsuccessful logon.

When an audit or noaudit statement is issued.

Explicit recompilation eliminates the need for implicit run-time recompilation and prevents associated run-time compilation errors and performance overhead. Triggers and Oracls Remote Exceptions A trigger that accesses a remote site cannot do remote exception handling if the network link is unavailable. The expression in a WHEN clause of a row trigger can include correlation names, which are explained later.

9 Using Triggers

You can retrieve each attribute with a function call. All other events fire the triggers in the existing user transaction.

The firing order of compound triggers is not guaranteed. Update cascade, update set null, update set default, delete set default, inserting a missing parent, and maintaining a count visparadores children can all be implemented easily.


Also, you can specify: If recompiling the trigger results in compilation errors, then the database returns an error and the trigger remains invalid. Just before the server starts the shutdown of an instance.

Auditing features enabled using the standard database features are easier to declare and maintain, and less prone to errors, when compared to auditing functions defined by triggers.

Check “Event Attribute Functions” before using an event attribute function, because its effects might be undefined rather than producing an error condition. For example, row triggers provide value-based auditing for each table row.

A procedure called by a trigger cannot run the previous transaction control statements, because the procedure runs within the context of the trigger body.

If an error occurs during the compilation of a trigger, the trigger is still created. For example, to disable the trigger named Reorderenter the following statement:. Triggers and declarative integrity constraints can both be used to constrain data input.

This type of trigger is useful to force values in specific columns that depend on the values of other columns in the same row.

Enabling and Disabling Triggers

The trigger cannot miss rows that have been changed but not committed by another transaction, because the foreign key constraint guarantees that no matching foreign key rows are locked before the after-row trigger is called. If there are five employees in department 20, then the trigger fires five times when this statement is entered, because five rows are affected.

When it detects an event, the database fires all triggers that are enabled on that event, except the following:. However, the AFTER row trigger fires once for each row of the table affected by the triggering statement, while the AFTER statement trigger fires only once after the triggering statement execution is completed.

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Creating a DDL Trigger: If this privilege is later revoked, you can drop the trigger but not alter it. The actions then insert new rows or update existing rows, as appropriate. You may need to set up data structures similar to the following for certain examples to work:.

Contraints and Triggers Triggers and declarative constraints can both be used to constrain data input. No action is required for inserts into the parent table no dependent foreign keys exist. However, when the view query gets complex, the system implicitly cannot translate the DML on the view into those on the underlying tables.

A trigger does not apply to data loaded before the definition of the trigger; therefore, it is not known if all data in a table conforms to the rules established by an associated trigger. For example, triggers can be used to enforce:. Certain DDL statements are executed for example: A system trigger is defined on a schema or the database.

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