ALTER TRIGGER

Purpose

Use the ALTER TRIGGER statement to enable, disable, or compile a database trigger.

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, you must have the ADMINISTER database events system privilege.

Syntax

alter_trigger::=

Description of the illustration alter_trigger.gif


compiler_parameters_clause::=

Description of the illustration compiler_parameters_clause.gif

Semantics

schema

Specify the schema containing the trigger. If you omit schema, then Oracle Database assumes the trigger is in your own schema.

trigger

Specify the name of the trigger to be altered.

ENABLE | DISABLE

Specify ENABLE to enable the trigger. You can also use the ENABLE ALL TRIGGERS clause of ALTER TABLE to enable all triggers associated with a table. See ALTER TABLE .

Specify DISABLE to disable the trigger. You can also use the DISABLE ALL TRIGGERS clause of ALTER TABLE to disable all triggers associated with a table.

RENAME Clause

Specify RENAME TO new_name to rename the trigger. Oracle Database renames the trigger and leaves it in the same state it was in before being renamed.

When you rename a trigger, the database rebuilds the remembered source of the trigger in the USER_SOURCE, ALL_SOURCE, and DBA_SOURCE data dictionary views. As a result, comments and formatting may change in the TEXT column of those views even though the trigger source did not change.

COMPILE Clause

Specify COMPILE to explicitly compile the trigger, whether it is valid or invalid. Explicit recompilation eliminates the need for implicit run-time recompilation and prevents associated run-time compilation errors and performance overhead.

Oracle Database first recompiles objects upon which the trigger depends, if any of these objects are invalid. If the database recompiles the trigger successfully, then the trigger becomes valid.

During recompilation, the database drops all persistent compiler switch settings, retrieves them again from the session, and stores them at the end of compilation. To avoid this process, specify the REUSE SETTINGS clause.

If recompiling the trigger results in compilation errors, then the database returns an error and the trigger remains invalid. You can see the associated compiler error messages with the SQL*Plus command SHOW ERRORS.

DEBUG

Specify DEBUG to instruct the PL/SQL compiler to generate and store the code for use by the PL/SQL debugger. Specifying this clause has the same effect as specifying PLSQL_DEBUG = TRUE in the compiler_parameters_clause.

compiler_parameters_clause

Use this clause to specify a value for one of the PL/SQL compiler parameters. The parameters you can specify in this clause are PLSQL_OPTIMIZE_LEVEL, PLSQL_CODE_TYPE, PLSQL_DEBUG, PLSQL_WARNINGS, and NLS_LENGTH_SEMANTICS.

You can specify each parameter only once in each statement. Each setting is valid only for the current library unit being compiled and does not affect other compilations in this session or system. To affect the entire session or system, you must set a value for the parameter using the ALTER SESSION or ALTER SYSTEM statement.

If you omit any parameter from this clause and you specify REUSE SETTINGS, then if a value was specified for the parameter in an earlier compilation of this library unit, Oracle Database uses that earlier value. If you omit any parameter and either you do not specify REUSE SETTINGS or no value has been specified for the parameter in an earlier compilation, then the database obtains the value for that parameter from the session environment.

Restriction on the compiler_parameters_clause

You cannot set a value for the PLSQL_DEBUG parameter if you also specify DEBUG, because both clauses set the PLSQL_DEBUG parameter, and you can specify a value for each parameter only once.

REUSE SETTINGS

Specify REUSE SETTINGS to prevent Oracle from dropping and reacquiring compiler switch settings. With this clause, Oracle preserves the existing settings and uses them for the recompilation of any parameters for which values are not specified elsewhere in this statement.

For backward compatibility, Oracle Database sets the persistently stored value of the PLSQL_COMPILER_FLAGS initialization parameter to reflect the values of the PLSQL_CODE_TYPE and PLSQL_DEBUG parameters that result from this statement.

Examples

Disabling Triggers: Example

The sample schema hr has a trigger named update_job_history created on the employees table. The trigger is fired whenever an UPDATE statement changes an employee's job_id. The trigger inserts into the job_history table a row that contains the employee's ID, begin and end date of the last job, and the job ID and department.

When this trigger is created, Oracle Database enables it automatically. You can subsequently disable the trigger with the following statement:

ALTER TRIGGER update_job_history DISABLE;
 

When the trigger is disabled, the database does not fire the trigger when an UPDATE statement changes an employee's job.

Enabling Triggers: Example

After disabling the trigger, you can subsequently enable it with the following statement:

ALTER TRIGGER update_job_history ENABLE; 

After you reenable the trigger, Oracle Database fires the trigger whenever an employee's job changes as a result of an UPDATE statement. If an employee's job is updated while the trigger is disabled, then the database does not automatically fire the trigger for this employee until another transaction changes the job_id again.