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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When a trigger encounters a mutating table, a runtime error occurs, the effects of the trigger body and triggering statement are rolled back, and control is returned to the user or application. Disparaddores defined using the standard constraint features are much easier to write and are less prone to errors, when compared with comparable constraints defined by triggers. Therefore, you can create disparaodres just not row triggers to read and modify the parent and child tables.
For example, suppose that a compound trigger is triggered by the following statement:. You can reference object columns or their attributes, or varray, nested table, or LOB columns. For example, do not assign a value to a global package variable in a row trigger if the current value of the global variable is dispardores on the row being processed by the row oeacle. Event Attribute Functions for information about event-specific attributes.
Compiled triggers have dependencies. For example, this trigger performs a complex check before allowing the triggering statement to run. Queries see the current read-consistent materialized view of referenced tables and any data changed within the same transaction. You should carefully test any triggers that require error trapping to succeed to ensure that they always work properly in your environment.
Before, after, each row and table level triggers [Oracle]
This type of trigger is useful to force values in specific columns that depend on the values of other columns in the same row. Two correlation names exist for every column of the table being modified: Given a position 1 for top of stackit returns the error message at that position on error stack.
Example Invoking a Java Subprogram from a Trigger.
When an event occurs, all triggers that are enabled on that event are fired, with some exceptions:. Name of the dictionary object on which the DDL operation occurred. You can dispardores a complex view over these tables to create a logical view of the library with sections and a collection of oracel in each section. These old and new values are: Compound Triggers A compound trigger can fire at more than one timing point.
A trigger is compiled when it is created. You might use the AFTER keyword if you want the trigger to query or change the same table, because triggers can only do that after the initial changes are applied and the table is back in a consistent state.
The parent row corresponding to this nested table element can be accessed using the parent qualifier.
This topic applies primarily to simple triggers. Triggers can also require the user to supply a “reason code” for issuing the audited SQL statement, which can be useful in both row and statement-level auditing situations. For example, do not assign a value to a global package variable in a row trigger if the current value of the global variable is dependent on the row being processed by the row trigger. A trigger is fired based on a triggering statementwhich specifies:.
Compound Trigger Example Scenario: 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 this is similar to the privilege model for stored subprograms. You may need to set up the following data structures for the examples to work: Trigger names must be unique with respect to other triggers in the same schema. Publish information about database events, user events, and SQL statements to subscribing applications.
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 Disparadorez DML operations against a table to those issued during regular business hours Enforce security authorizations Prevent invalid transactions Caution: When an audit or noaudit statement is issued.
Each subsequent trigger sees the changes made by disparadored previously fired triggers. However, you cannot change the values of these columns in the body of the trigger itself. These triggers can be defined over views, and they fire oarcle of the actual DML.
Enabling and Disabling Triggers
However, starting in Oracle Database release 8. The size of the trigger cannot be more than 32K. For example, triggers can be used to enforce:. The following sections use this example to illustrate the way that parts of a trigger are specified. If the trigger issues SQL statements or calls procedures or functions, then the owner of the trigger must have the privileges necessary disparadorfs perform these operations. The mutating error, discussed earlier in this section, still prevents the trigger from reading or disparadorws the table that the parent statement is modifying.
They become invalid if a depended-on object, such as a stored procedure or function called from the trigger body, is modified. Also, if global package variables are updated within a trigger, then it is best to initialize those variables in a BEFORE statement trigger.
For example, a table and a disparsdores can have the same name however, to avoid confusion, this is not recommended.
For example, assume a trigger is defined as the following:. Specify one or more types of DDL statements that can cause the trigger to fire. Error Disparasores Return status from publication callout functions for all events are ignored.