I use DB2 Express-C.
I have ON INSERT trigger on a table, where I insert the new row into another table.
Is there a way not to insert the new row into the table on which the trigger is defined?
Any help is appreciated, thank you
Take a look at create trigger and the INSTEAD OF option:
Specifies that the associated triggered action replaces the action
against the subject view. Only one INSTEAD OF trigger is allowed for
each kind of operation on a given subject view (SQLSTATE 428FP).
Typically something like this can be done by evaluating whether a special register (e.g., CURRENT USER) has a particular value.
create trigger trigger1
after insert on schema.table
referencing new as n
for each row
when (CURRENT USER <> 'NAMSARAY')
insert into schema.tablecopy values (n.c1, n.c2, ...);
If you are on DB2 9.7 or later, you could also consider defining a variable and using that variable as a control of whether or not the trigger will perform its action.
create variable schema.var1 smallint default 0;
Then you can check the value of this variable in the trigger. Unless an application has explicitly set the variable to a predetermined value (-9999 in the example below), the trigger will fire:
create trigger trigger2
after insert on schema.table
referencing new as n
for each row
when (schema.var1 <> -9999)
insert into schema.tablecopy values (n.c1, n.c2, ...);
Related
So I am new to using procedures and triggers and it is really confusing me
I have used temporal tables and want to basically create a history table of records inserted,updated or deleted.
Infact I have created my history table and works fine when I use this trigger sql
DROP TRIGGER if exists versioning_trigger on mytable;
CREATE TRIGGER versioning_trigger BEFORE INSERT OR UPDATE OR DELETE ON mytable FOR EACH ROW EXECUTE PROCEDURE versioning('sys_period', 'table_history', true);
This creates records of the rows updated or deleted,precisely copies the old row record from mytable into table_history table and updates the record in mytable.But I want to insert the updated record from mytable to table_history also so that it has records of all types('current active record'and 'record before updation').Also insert some other fields in table_history when the trigger is executed.
I want to ask
How is it possible to have different trigger events(BEFORE or AFTER) together in one CREATE TRIGGER query in temporal_tables?
Is it possible to insert new field values in table_history on trigger execution? How can I accomplish this?
https://www.postgresql.org/docs/current/static/plpgsql-trigger.html
A trigger procedure is created with the CREATE FUNCTION command,
declaring it as a function with no arguments and a return type of
trigger
and also
same trigger can't fire both before and after event - just create two triggers if you really need it
https://www.postgresql.org/docs/current/static/sql-createtrigger.html
Determines whether the function is called before, after, or instead of
the event.
use NEW instead of OLD for new values
https://www.postgresql.org/docs/current/static/plpgsql-trigger.html
NEW
Data type RECORD; variable holding the new database row for
INSERT/UPDATE operations in row-level triggers. This variable is
unassigned in statement-level triggers and for DELETE operations.
Situation
I have a database in PostgreSQL 9.5 used to store object locations by time.
I have a main table named "position" with the columns (only relevant):
position_id
position_timestamp
object_id
It is partitioned into 100 child tables on object_id with the condition:
CREATE TABLE position_object_id_00
( CHECK object_id%100 = 0 )
INHERITS ( position );
And so on for the others children. I partitioned with a modulus relation to distribute equally the objects.
Each child is indexed on position_id and object_id (two different indexes).
The trigger to redirect inserts on children is:
CREATE TRIGGER insert_position_trigger
BEFORE INSERT ON position
FOR EACH ROW EXECUTE PROCEDURE insert_position();
And the procedure insert_position() looks for the right child table to insert the data, inserts it and then return the NEW object:
CREATE OR REPLACE FUNCTION insert_position() RETURNS TRIGGER AS $insert_position$
DECLARE
BEGIN
--Look for child table
[...]
--Insert data in right child table
[...]
RETURN NEW;
END;
$insert_position$ LANGUAGE plpgsql;
I have a summary table object_last_known_position with the same columns that is updated with the trigger:
CREATE TRIGGER update_object_last_known_position
AFTER INSERT OR UPDATE ON position
FOR EACH ROW
EXECUTE PROCEDURE update_object_last_known_position();
The procedure update_object_last_known_position() basically checks if the position_timestamp is more recent, then delete the older entry and create a new entry with the data passed on the INSERT or UPDATE query (NEW).
Issue
So these two triggers react to the same event: insert on position, one is before, the other is after
Returning new for insert_position() allows me to use NEW in the trigger update_object_last_known_position(), and this is absolutely necessary. But doing that, it also insert the data on the master table position. So my data is now duplicated.
I tried to put the two triggers before, they both execute when I insert data if I let it like that, but if I remove the "return new" from the procedure insert_position(), update_object_last_known_position() is not executed.
I am stuck with this issue and I didn't find a way to execute both of these triggers without filling the master table position when I insert data.
So if you have any ideas, I will really appreciate :)
Thank you for your help!
EDIT
Solution
Thanks to the answer
I "merged" my two triggers: insert_position() now calls update_object_last_known_position directly. For that, I modified update_object_last_known_position to a stored procedure with a parameter. The parameter is the id of the position insert_position() just created, so I am able to find it and retrieve information.
(Calling update_object_last_known_position inside the other trigger means we cannot use NEW anymore)
And obviously return type for insert_position() is now NULL, and everything works fine :)
If I understand you correctly you are trying to:
Stop the insert, and replace it with an insert into another table (determined by the trigger)
Update a summary table (delete/insert) to point to the new row.
Your problem is that 1 stops 2 from happening? That's logical because you've stopped the insert so you've stopped any processing on the insert as well.
So to solve this you have a couple of options (options 1 and 2 are similar)
Call update_object_last_known_position() from insert_position() and only have one trigger
Create a wrapper method for both insert_position() and update_object_last_known_position() and have only one trigger.
Put the trigger for update_object_last_known_position() on all of the tables that insert_position() might insert into.
In PostgreSQL 9.1, I need to assign another field in a table with the same value of the ID column which is serial.
For now I'm adding a RETURNING part to INSERT command and use a successive UPDATE command to update the record in the same transaction.
I'd really like to perform this operation in the same transaction and preferably same SQL command (without the need to resort to after insert triggers).
My question is inside the before insert trigger on the same table, is the NEW variable which is supposed to contain the record which is about to be inserted, already initialized with the return value of nextval('seq_table') for the id field or not?
Can I assign this value to another field in the same trigger function? is this valid?
NEW.custom_field := NEW.id;
I'm looking for a way to manipulate rows automatically before adding them to a table in postgreSQL. Say for instance we have the following table:
CREATE TABLE foo (
id serial NOT NULL,
value integer NOT NULL,
CONSTRAINT "Foo_pkey" PRIMARY KEY (id),
CONSTRAINT "Foo_value_check" CHECK (value >= 0)
)
Now one can insert rows:
INSERT INTO foo (id,value) VALUES ('0','2')
And when one enters:
INSERT INTO foo (id,value) VALUES ('1','-2')
An error will occur. Is it possible to define a "rewrite rule" that given the value column contains a value less than zero, zero is used (for instance)?
Yes, it is possible. One way is to use triggers. A trigger causes a procedure to be run on particular actions, which can allow you to modify the data to be inserted (amongst other things).
To set up a trigger, you first create a function that will perform the checks and modifications you want. The variable new in your function will be implicitly declared and contain the new row to be inserted / updated so you can check and modify the values before they reach the table.
You then specify that this function is to be called before insert or update on one or more tables.
Example:
CREATE FUNCTION validate_foo_row()
RETURNS TRIGGER AS $$
BEGIN
IF new.value<0 THEN
new.value=0;
END IF;
RETURN NEW;
END
$$ LANGUAGE 'plpgsql';
CREATE TRIGGER trig_validate_foo BEFORE INSERT ON foo
FOR EACH ROW EXECUTE PROCEDURE validate_foo_row();
SqlFiddle Here
The above simplistic example only triggers for inserts, you might want to have it trigger for updates as well.
You can read more about triggers in the postgresql manual. They are powerful and are capable of a lot more than this simple example shows.
I want to create a trigger, somehow like this:
CREATE TRIGGER foo
AFTER UPDATE OR INSERT ON bar
FOR EACH ROW EXECUTE PROCEDURE baz(NEW.id);
The part with NEW.id doesn't work. How can I send values from the changed row (id for instance) to the trigger-function.
The trigger function (procedure) knows NEW and OLD automatically. No need to pass those as parameters.
Read more in the chapter on Trigger Procedures in the manual:
When a PL/pgSQL function is called as a trigger, several special
variables are created automatically in the top-level block. They are:
NEW
Data type RECORD; variable holding the new database row for INSERT/UPDATE operations in row-level triggers. This variable is NULL
in statement-level triggers and for DELETE operations.