I have condition to insert record in table for that i want to write trigger.
For an instance : when A code is getting inserted in the table at the same time insert B code as well in that table.
Need trigger query
Related
I have a problem with trigger created to invoke before insert method.
For example, i have 3 columns in my table and 1 of these columns is inserted by trigger.
When i want to insert all data(into all columns) by myself trigger overwrites data in specified column.
The trigger is specified to invoke before insert command so i though that insert command will overwrite data in column specified in trigger.
Do anyone know how to solve this issue?
Is this possible for me to insert all data by myself when i have created a trigger?
I have created a trigger and was expecting a mutating table error in below case but didn't get one through normal insert but getting an error while inserting using a query. I am not sure which concept I am missing here.
drop table temp;
create table temp (id number,name varchar2(500),is_active number);
create or replace trigger temp_trg before insert on temp
for each row
declare
v_count number;
begin
select count(1) into v_count from temp;
update temp set is_active=0 where is_active=1 and id=:new.id;
end;
/
select * from temp;
insert into temp values (1,'xyz',1);
insert into temp values (1,'xyz',1);
insert into temp select 1,'xyz',1 from dual;
getting an error while inserting using a query.
Mutating table occurs when we query the table which owns the trigger. Specifically it happens when Oracle can't guarantee the outcome of the query. Now when you insert a single row into the table Oracle can predict the outcome of the query when the FOR EACH ROW trigger fires, because it's a single row.
But with an INSERT FROM query Oracle is confused: should the count be the final figure including all the rows selected by the query or just a rolling count? The answer seems straightforward in this case but it's easy to imagine other queries where the answer is not clear cut. Rather than evaluate each query on its predictability Oracle enforces a plain fiat and hurls ORA-04091 for all query driven inserts.
The restriction on Mutating Tables applies to all triggers that use FOR EACH ROW clause except when either of the following is true:
the trigger fires on BEFORE event, i.e. the data wasn't actually changed
it is known that only one row will be affected - INSERT ... VALUES is the only DML that meets this condition
I have a trigger that is fire on inserting a new record in table in that i want to insert new record in the same table.
My trigger is :
create or replace trigger inst_table
after insert on test_table referencing new as new old as old
for each row
declare
df_name varchar2(500);
df_desc varchar2(2000);
begin
df_name := :new.name;
df_desc := :new.description;
if inserting then
FOR item IN (SELECT pid FROM tbl2 where pid not in(1))
LOOP
insert into test_table (name,description,pid) values(df_name,df_desc,item.pid);
END LOOP;
end if;
end;
its give a error like
ORA-04091: table TEST_TABLE is mutating, trigger/function may not see it
i think it is preventing me to insert into same table.
so how can i insert this new record in to same table.
Note :- I am using Oracle as database
Mutation happens any time you have a row-level trigger that modifies the table that you're triggering on. The problem, is that Oracle can't know how to behave. You insert a row, the trigger itself inserts a row into the same table, and Oracle gets confused, cause, those inserts into the table due to the trigger, are they subject to the trigger action too?
The solution is a three-step process.
1.) Statement level before trigger that instantiates a package that will keep track of the rows being inserted.
2.) Row-level before or after trigger that saves that row info into the package variables that were instantiated in the previous step.
3.) Statement level after trigger that inserts into the table, all the rows that are saved in the package variable.
An example of this can be found here:
http://asktom.oracle.com/pls/asktom/ASKTOM.download_file?p_file=6551198119097816936
Hope that helps.
I'd say that you should look at any way OTHER than triggers to achieve this. As mentioned in the answer from Mark Bobak, the trigger is inserting a row and then for each row inserted by the trigger, that then needs to call the trigger to insert more rows.
I'd look at either writing a stored procedure to create the insert or just insert via a sub-query rather than by values.
Triggers can be used to solve simple problems but when solving more complicated problems they will just cause headaches.
It would be worth reading through the answers to this duplicate question posted by APC and also these this article from Tom Kyte. BTW, the article is also referenced in the duplicate question but the link is now out of date.
Although after complaining about how bad triggers are, here is another solution.
Maybe you need to look at having two tables. Insert the data into the test_table table as you currently do. But instead of having the trigger insert additional rows into the test_table table, have a detail table with the data. The trigger can then insert all the required rows into the detail table.
You may again encounter the mutating trigger error if you have a delete cascade foreign key relationship between the two tables so it might be best to avoid that.
I have a database with tables that are chained together with foreign keys, and the last one in the chain also has a foreign key to itself. I want to delete them with cascade on, exapt for the last one in the chain. That one should be set null, unless it's parent record has a certain value. I figured i would do that with a trigger: whenever the last table updated, if the foreign key to itself had been set to null, check the field in the parent record, and if it is the value "default", delete the record in the last table.
However, I haven't found any help online indicting that comparing a parent record in another table.
Is this possible?
In general, a row-level trigger on table A cannot query table A. Doing so would generally raise a mutating table exception (ORA-04091). So a trigger is generally not the right solution.
Presumably, you have some sort of API (i.e. a stored procedure) to delete records from the parent table. That API should query this last table before issuing the DELETE against the parent table. It should take care of updating the last table in the chain as well as deleting the data from the parent table.
If you really wanted a trigger-based solution, life would get substantially more complicated. You could work around the mutating table exception by
Creating a package with a collection of primary keys from the parent table
Creating a before statement trigger that initializes this collection
Creating a row-level trigger that populates the collection with the primary keys that were modified by the SQL statement
Creating an after statement trigger that iterates over the collection and issues whatever DML is necessary (unlike row-level triggers, statement-level triggers on table A can query or modify table A).
If you're using 11g, you can simplify this a bit with a compound trigger with before statement, after row, and after statement sections. But you've still got a number of moving pieces to try to coordinate.
AFAIK you won't be able to really delete the record in the last table (mutating table problem), but you could update a status field indicating the record has been logically deleted (untested):
create or replace trigger last_table_trig
before update on last_table
for each row
declare
l_parentField varchar2(100);
begin
if :new.self_ref_fk is null then
select p.parent_field into l_parentField from parent_table p
where p.pk = :new.parent_fk;
if l_parentField = 'default' then
:new.status := 'DELETED';
end if;
end if;
end;
I have a TABLE1. On this table I created a trigger : AFTER INSERT OR UPDATE OR DELETE
Now, if I do an insert which doesn't insert anything, the trigger will still be fired :
insert into TABLE1 select * from TABLE1 where 1=0;
This query will insert NO ROWS but yet the trigger is still fired.
Is there a way to avoid this ? Is this normal behavior?
Yes, it is normal behaviour. It can be avoided, though doing so requires having 3 triggers:
A BEFORE trigger to set a package boolean variable to FALSE
A FOR EACH ROW trigger to set the variable to TRUE when a row is inserted
The AFTER trigger you have, where you can now check the value of the variable before carrying out its action.
Sounds like overkill? Maybe it is: what are to trying to achieve with your trigger?
This is the normal behaviour, Oracle is expecting to insert row so it fires both BEFORE INSERT and AFTER INSERT triggers, even if no row is inserted. One of the purpose of the AFTER triggers is to do some action after a statement succeeds. This statement succeeded :)
You could count the number of rows affected with a package variable:
set the mypackage.table1_nb_ins variable to 0 in a BEFORE INSERT trigger
increment the counter in a AFTER INESRT FOR EACH ROW trigger
and then perform your AFTER INSERT logic if your counter is greater than 0
Row Triggers
A row trigger is fired each time the table is affected by the triggering statement. For example, if an UPDATE statement updates multiple rows of a table, a row trigger is fired once for each row affected by the UPDATE statement. If a triggering statement affects no rows, a row trigger is not run.
https://docs.oracle.com/cd/B19306_01/server.102/b14220/triggers.htm