I am new to Triggers in database and ECA.
According to my understanding, Triggers are the automated procedures in PL/SQl that are fired based upon some Event and Condition which is provide by ECA.
But does ECA has its own independent significance in database, it some independent system? or How do Triggers and ECA relate to each other ?
Any help on the above topics is highly appreciated .
Triggers mechanism allows to bind custom procedures to low level DML operations like insert, update and delete. Procedures are created by language used by data base, for example: oracle uses pl/sql, sql server uses tsql and other can use others.
For example:
Developer can create trigger on delete operation on table customers that invoke procedure that create log.
You can say Trigger is fulfilling ECA concept.
Event - is DML operation on data.
Condition - defined during trigger creation.
Action - procedure defined by developer.
Related
I have around 500 tables in DB. If there is any DML operations performed on that table then trigger should be fired to capture those dml activities and should load it into an audit table. I dont want to write 500 individual triggers. Any simple method to achieve this?
To switch all high level auditing of DML statements for all tables:
AUDIT INSERT TABLE, UPDATE TABLE, DELETE TABLE;
What objects we can manage depends on what privileges we have. Find out more.
AUDIT will write basic information to the audit trail. The destination depends on the value of the AUDIT_TRAIL parameter. If the parameter is set to db the output is written to a database table: we can see our trail in USER_AUDIT_TRAIL or (if we have the privilege) everything in DBA_AUDIT_TRAIL.
The audit trail is high level, which means it records that user FOX updated the EMP table but doesn't tell us which records or what the actual changes were. We can implement granular auditing by creating Fine-Grained Audit policies. This requires a lot more work on our part so we may decide not to enable it for all our tables. Find out more.
Triggers are used on tables only, not the entire database. Ignoring the complexity of maintaining disparate data types, data use, context of various tables and their use, what you are looking for would be extremely complex, something no RDBMS has addressed at the database level.
There is some information on triggers at this link:
https://docs.oracle.com/cd/A57673_01/DOC/server/doc/SCN73/ch15.htm
You could place a trigger on each table that calls the same procedure ... but then all that complexity comes into play.
Like in procedures and Functions can we pass parameters to triggers? Can A trigger can be explicitly called?
An object based trigger is raised by an event's occurence(as update,insert,select)on a specific object of the database. There is also system triggers, fired by system specific events(as shutdown,startup database, user connection etc..).
This is the main purpose of a trigger in databases, you can't raise it explicitly, if you want it to run the only way is to raise the event. Also passing parameters isn't part of trigger definition, but you can handle the event attributes,(which can be passed to the trigger body that may can contain functions or procedures).
I hope that i've responded to your question, can i know what is your need for trying to do that.?
What you can do is to create a table that will store temporarily the data that you want to access in your trigger.
1-Create a table "tmp_data" for instance.
2-Before running the event that will fire the trigger (stored procedure, insert, update...) insert into tmp_data the data that you want to use in the trigger.
3-In the trigger, to access the data you needed, you make a query on the table tmp_data.
4-After have been done with the data, you clean the table tmp_data for the next use.
Hope has been helpful!
Can anyone suggest a good event pattern design or framework for changes in table in oracle.
Changes are not just the based on the column value change,but also the business driven logic .All the logging should be driven by some event setup.
At the end we track the changes and drive the business logic based on the changes .
I might be talking too high level,sorry for that :)
Assume TableA needs to be tracked for ColumnA.
Create AUDIT_TRAIL Table with columns TABLENAME, COLUMNNAME, OLDVALUE,NEWVALUE, DATEANDTIME, PK_SEQ
Create a Trigger to poll TableA for any change in ColumnA, and insert them into AUDIT_TRAIL (PK_SEQ should be a Oracle Sequence Number, DATEANDTIME should be from sysdate)
Something like this for trigger
CREATE OR REPLACE TRIGGER trg_table_audit
before insert or update or delete on tableA REFERENCING NEW AS NEW OLD AS OLD
for each row
begin
if inserting or deleting then
insert into audittrail (....)
Reading the fine manual: Using Triggers to Write Audit Data to a Separate Table:
You can use triggers to supplement the built-in auditing features of Oracle Database. The trigger that you create records user actions to a separate database table. When an activity fires the trigger, the trigger records the action in this table. Triggers are useful when you want to record customized information such as before-and-after changes to a table.
Reading even more the fine manual: PL/SQL Triggers:
A trigger is like a stored procedure that Oracle Database invokes automatically whenever a specified event occurs.
On top of that you can build a setup engine that turns triggers on and off. The "business logic" can later read the data recorded by the triggers.
I assume you're not interested in auditing. For the details see e.g. Verifying Security Access with Auditing.
How about you start with using TRIGGERS? And then from there, you could call procedures/functions from a package body for tracking the changes on the table/s.
I have an Oracle trigger which is calling a stored procedure that has PRAGMA AUTONOMOUS_TRANSACTION defined. The values that are passed from the trigger have been committed already but it appears that the values are not available in the stored procedure? I'm not positive of this since the ability to debug/log/commit is difficult and the timing of the output is confusing me a bit. I'd like to know if it's expected that any passed values are simply available in the stored procedure regardless of the AUTONOMOUS_TRANSACTION?
Thanks
Values passed in to a stored procedure as parameters will always be available to the stored procedure. It doesn't matter whether the procedure is declared using an autonomous transaction.
Code running in an autonomous transaction cannot see changes made by the calling transaction. 9 times out of 10, when people are describing problems seeing the data they expect, this is the source of the problem.
If your stored procedure is doing anything other than writing something to a log table, I would be exceptionally cautious about using autonomous transactions. If you are using autonomous transactions for anything other than logging, you are almost certainly using them incorrectly. And you are probably introducing a whole host of bugs related to race conditions and transactional integrity.
"The trigger logic is conditionally
updating Table B which calls the
stored procedure to select from the
values on Table A so that Table B can
be updated with a calculated value. "
Perhaps Table B really ought to be a Materialized View derived from Table A? We can build a lot of complexity into the WHERE clauses of the queries which populate MViews. Find out more.
If you have a row level trigger on table_x, then that trigger can be fired multiple times by the same statement as different rows are impacted by that statement.
The order in which those rows are impacted is indeterminate. As such, the state of table_x is indeterminate during the execution of a row level trigger. This is why the MUTATING TABLE exception is raised.
An autonomous transaction 'cheats' by looking at the committed state of the table (ie excluding all changes made by that statement, and other statements in the transaction).
If you want a stored procedure to look at the state of table_x in response to activity on that table, then it needs to be done after all the rows changes have been made (ie in a statement level trigger, not a row level trigger).
The design pattern for this is often to set a flag (package level variable) in a row level trigger, check the flag in an AFTER statement level trigger, and if necessary action it and reset it.
I created the Employee table which contains EmpNo,EName,EDesignation as its fields.Also i created the 3 Triggers namely Trigger_1,Trigger_2 and Trigger_3.All the Triggers are Statement level triggers and fired after the update done in the table.Now i want the following orders in which the triggers are going to fired when the update statement is executed.
The Order is
Trigger_3,
Trigger_1,
Trigger_2
Can anyone tell me the way to fire the trigger events in userdefined way?I m using Oracle 9i
Trigger Evaluation Order
Quote from Oracle documentation:
Although any trigger can run a
sequence of operations either in-line
or by calling procedures, using
multiple triggers of the same type
enhances database administration by
permitting the modular installation of
applications that have triggers on the
same tables.
Oracle Database executes all triggers
of the same type before executing
triggers of a different type. If you
have multiple triggers of the same
type on a single table, then Oracle
Database chooses an arbitrary order to
execute these triggers.
Each subsequent trigger sees the
changes made by the previously fired
triggers. Each trigger can see the old
and new values. The old values are the
original values, and the new values
are the current values, as set by the
most recently fired UPDATE or INSERT
trigger.
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).
see also http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14251/adfns_triggers.htm
Have one trigger with the contents of the three.
If you cannot, for reasons for modularization, reusability..., create three stored procedures and call these one by one in the single trigger.
Upgrade to 11g and you can define trigger execution order