I have a trigger with before insert option and inside the trigger I insert the data to the same table. How would SQL handle this kind of issues as this lead to creating infinite triggers.
For Example:
Create trigger trigger_name on Employee
before insert
as
insert on table Employee values(1001, 'chas');
go
Thanks for the help
Related
I would like to create trigger to execute function to truncate local database table and insert new data.
Trigger execution must start after new row have insert in foreign database table.
I have read a lot about creating triggers on foreign table, but for me its not working. Trigger seems to not execute function when new row will be inserted in foreign table. It seems like trigger cant see this new row insert event.
What I did:
Created foreign table in my local database, lets call it 'foreign_table'. I tested, I can read data.
Created function to truncate local table and insert new data:
CREATE or replace FUNCTION public.reset_insert_table()
RETURNS TRIGGER
LANGUAGE 'plpgsql'
SET search_path=public
AS $BODY$
BEGIN
create temporary table temporary_table_tmp
as select * from public.table1;
TRUNCATE TABLE public.table2;
insert into table2
select * from temporary_table_tmp;
DROP table temporary_table_tmp;
END;
$BODY$;
Created trigger to launch function 'reset_insert_table()'
CREATE TRIGGER local_table_update
AFTER INSERT
ON 'foreign_table'
FOR EACH ROW EXECUTE PROCEDURE reset_insert_table();
Made test: inserted new row in foreign database table 'foreign_table', but I cant see that table is truncated and new data is not inserted. Insertion to foreign_tale was done in foreign database.
Problem was also testing does this trigger function work, executing manually will produce error:
EXECUTE PROCEDURE reset_insert_table();
ERROR: syntax error at or near "execute"
Tried also CALL and SELECT.
I created same function for testing but instead defining 'RETURNS TRIGGER'used 'RETURNS VOID' and function is working.
Can anyone tell why my solution is not working and does trigger on foreign tables must see events happening in foreign tables?
According to your comments, you seem to be using logical replication.
While data modifications are replayed on the standby with logical replication, the parameter session_replication_role is set to replica to keep triggers and foreign key constraints from working.
If you want a trigger to be triggered by the replay of data via logical replication, you have to declare it as a replica trigger:
ALTER TABLE a2 ENABLE REPLICA TRIGGER trigger_name;
I'm using a PostgreSQL RDS instance in AWS. Basically, there is a query that inserts data into a first table, let's call it table. The data there can have duplicates in some fields (except for the primary key obviously).
Then there is the trigger that updates another table, infotable, allowing no duplicates.
The trigger:
CREATE TRIGGER insert_infotable AFTER INSERT ON table
FOR EACH ROW EXECUTE PROCEDURE insert_infotable();
The relevant part of the trigger function looks like this:
CREATE OR REPLACE FUNCTION insert_infotable() RETURNS trigger AS $insert_infotable$
BEGIN
--some irrelevant code
IF NOT EXISTS (SELECT * FROM infotable WHERE col1 = NEW.col1 AND col2 = NEW.col2) THEN
INSERT INTO infotable(col1, col2, col3, col4, col5, col6) values (--some values--);
END IF;
RETURN NEW;
END;
$insert_infotable$ LANGUAGE plpgsql;
The table infotable has a UNIQUE constraint on the columns col1 and col2.
In general all is working fine, but rarely, about once in 1k inserts, the trigger returns an error 'duplicate key value violates unique constraint "unique_col1_and_col2"' for table infotable. Which shouldn't happen since there is the IF NOT EXISTS part in the trigger function.
The first question is what might be the cause of this? The only thing I can think of is races where two users are getting the same info simultaneously, both trigger the trigger but then one updates the second table via trigger and the second user gets the duplicate error. And because of that his whole insert query fails, including the insert to the main table.
If that's the case, what can I do about it? Is using a lock on insert a good idea for a table that is supposed to have 100+ users inserting data simultaneously?
And if yes, what type of lock should I use and what table should I lock -- the main table, or the second one, which gets modified by the trigger? (or I guess should I have the lock with my main insert statement or inside the trigger function?)
Yes, this is a race condition. Two such triggers running concurrently won't see each other's modifications, because the transactions are not yet committed.
Since you have a unique constraint on infotable, you can simply use
INSERT INTO infotable ...
ON CONFLICT (col1, col2) DO NOTHING;
I have an active trigger for myTable which should get fired after insert for each row. When I insert something into myTable by doing:
insert into myTable(column1) values(1);
The trigger gets fired, however if I insert values with
insert into myTable(column1) select column1 from otherTable limit 1;
The trigger does not fire at all, even though the value gets inserted into myTable. In my opinion it shouldnt matter which way gets the data inserted into myTable.
This is my trigger ddl
CREATE TRIGGER myTrigger
AFTER INSERT
ON myTable
FOR EACH ROW
EXECUTE PROCEDURE myProcedure();
Am I not understanding something crucial here?
Oh, and im on PostgreSQL 9.5
I am creating a control table in a PostgreSQL database, this table should register the query that fired a trigger in a specific table. For instance
if I do
insert into employees('bob');
I would like to be able to capture the string 'insert into employees('bob');' inside a trigger associated with employees table. It doesn't matter if the trigger is before or after.
Use the function current_query() in the trigger function.
insert into control_table(query_text)
select current_query();
The trigger should be for each statement.
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.