I have a table in postgres 9.4 and I need to do the following:
When new inserted record comes, I need to find previous records with given parameters and assign it's 'next_message' column value to newly generated record. So I want each record had reference to the next one with given filter, for example 'session_id'. So, if session_id=5, all records with seesion_id=5 should reference next one. I created a trigger that selects previous record and set this field. But it's bad and it will not work in highly loaded db table. How to do that?
That's my trigger:
CREATE OR REPLACE FUNCTION "public"."messages_compute_next_message" () RETURNS trigger
VOLATILE
AS $dbvis$
DECLARE previous_session_message integer;
BEGIN
/*NEW.next_message_id=NEW.id;*/
update message set next_message_id=NEW.id where id=(select max(c.id) from message c where c.session_id=NEW.session_id and c.id<>NEW.id);
RETURN NEW;
END
$dbvis$ LANGUAGE plpgsql
If I post records too frequently, I get many null values in next_message_id fields. And it's logical, otherwise I have to block entire table on every insert. How to do that properly in postgres?
I'd say forget about next_message_id.
The way your trigger looks, it seems to me that messages are ordered by id within one session.
So if you need the previous message for the message with id 42, you can find it with
SELECT max(prev.id)
FROM message prev JOIN message curr
ON prev.session_id = curr.session_id
AND prev.id < curr.id
WHERE curr.id = 42;
Setting the right indexes will speed this up considerably.
I assume there already is an index on id; maybe a second index ON (session_id, id) will help.
Related
I have to check when a table is inserted to/updated to see if a column value exists for the same HotelID and different RoomNo in the same table. I'm thinking that an INSTEAD OF trigger on the table would be a good option, but I read that it's a bad idea to update/insert the table the trigger executes on inside the trigger and you should create the trigger on a view instead (which raises more questions for me)
Is it ok to create a trigger like this? Is there a better option?
CREATE TRIGGER dbo.tgr_tblInterfaceRoomMappingUpsert
ON dbo.tblInterfaceRoomMapping
INSTEAD OF INSERT, UPDATE
AS
BEGIN
SET NOCOUNT ON;
DECLARE #txtRoomNo nvarchar(20)
SELECT #txtRoomNo = Sonifi_RoomNo
FROM dbo.tblInterfaceRoomMapping r
INNER JOIN INSERTED i
ON r.iHotelID = i.iHotelID
AND r.Sonifi_RoomNo = i.Sonifi_RoomNo
AND r.txtRoomNo <> i.txtRoomNo
IF #txtRoomNo IS NULL
BEGIN
-- Insert/update the record
END
ELSE
BEGIN
-- Raise error
END
END
GO
So it sounds like you only want 1 row per combo of HotelID and Sonifi_RoomNo.
CREATE UNIQUE INDEX UQ_dbo_tblInterfaceRoomMapping
ON dbo.tblInterfaceRoomMapping(HotelID,Sonifi_RoomNo)
Now if you try and put a second row with the same values, it will bark at you.
It's (usually) not okay to create a trigger like that.
Your trigger assumes a single row update or insert will only ever occur - is that guaranteed?
What will be the value of #txtRoomNo if multiple rows are inserted or updated in the same batch?
Eg, if an update is performed against the table resulting in 1 row with correct data and 1 row with incorrect data, how do you think your trigger would cope in that situation? Remember triggers fire once per insert/update, not per row.
Depending on your requirments you could keep the instead of trigger concept, however I would suggest a separate trigger for inserts and for updates.
In each you can then insert / update and include a where not exists clause to only allow valid inserts / updates, ignoring inserting or updating anything invalid.
I would avoid raising an error in the trigger, if you need to handle bad data you could also insert into some logging table with the reverse where exists logic and then handle separately.
Ultimately though, it would be best for the application to check if the roomNo is already used.
I am trying to write a trigger which gets data from the table attribute in which multiple rows are inserted corresponding to one actionId at one time and group all that data into the one object:
Table Schema
actionId
key
value
I am firing trigger on rows insertion,SO how can I handle this multiple row insertion and how can I collect all the data.
CREATE TRIGGER attribute_changes
AFTER INSERT
ON attributes
FOR EACH ROW
EXECUTE PROCEDURE log_attribute_changes();
and the function,
CREATE OR REPLACE FUNCTION wflowr222.log_task_extendedattribute_changes()
RETURNS trigger AS
$BODY$
DECLARE
_message json;
_extendedAttributes jsonb;
BEGIN
SELECT json_agg(tmp)
INTO _extendedAttributes
FROM (
-- your subquery goes here, for example:
SELECT attributes.key, attributes.value
FROM attributes
WHERE attributes.actionId=NEW.actionId
) tmp;
_message :=json_build_object('actionId',NEW.actionId,'extendedAttributes',_extendedAttributes);
INSERT INTO wflowr222.irisevents(message)
VALUES(_message );
RETURN NULL;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
and data format is,
actionId key value
2 flag true
2 image http:test.com/image
2 status New
I tried to do it via Insert trigger, but it is firing on each row inserted.
If anyone has any idea about this?
I expect that the problem is that you're using a FOR EACH ROW trigger; what you likely want is a FOR EACH STATEMENT trigger - ie. which only fires once for your multi-line INSERT statement. See the description at https://www.postgresql.org/docs/current/sql-createtrigger.html for a more through explanation.
AFAICT, you will also need to add REFERENCING NEW TABLE AS NEW in this mode to make the NEW reference available to the trigger function. So your CREATE TRIGGER syntax would need to be:
CREATE TRIGGER attribute_changes
AFTER INSERT
ON attributes
REFERENCING NEW TABLE AS NEW
FOR EACH STATEMENT
EXECUTE PROCEDURE log_attribute_changes();
I've read elsewhere that the required REFERENCING NEW TABLE ... syntax is only supported in PostgreSQL 10 and later.
Considering the version of postgres you have, and therefore keeping in mind that you can't use a trigger defined FOR EACH STATEMENT for your purpose, the only alternative I see is
using a trigger after insert in order to collect some information about changes in a utility table
using a unix cron that execute a pl/sql that do the job on data set
For example:
Your utility table
CREATE TABLE utility (
actionid integer,
createtime timestamp
);
You can define a trigger FOR EACH ROW with a body that do something like this
INSERT INTO utilty values(NEW.actionid, curent_timestamp);
And, finally, have a crontab UNIX that execute a file or a procedure that to something like this:
SELECT a.* FROM utility u JOIN yourtable a ON a.actionid = u.actionid WHERE u.createtime < current_timestamp;
// do something here with records selected above
TRUNCATE table utility;
If you had postgres 9.5 you could have used pg_cron instead of unix cron...
A trigger fires on a table, but the select on the table returns null. How can I create the code to be able to access the row that fired the trigger?
I have the following in the trigger:
begin
dws_edi_api.init_edi_message(message_id,order_no',supplier_no');
end;
This fires on update of the column row_state in the table out_message_tab
The event fires OK but when in the procedure dws_edi_api.init_edi_message_line I do a select c08 from out_message_tab where message_id = message_id_ (variable from the trigger). it returns null.
I assume the change hasnt been committed. I have tried adding a commit as the first line in my code to force the change to commit but that doesnt help. I have tried adding a dbms_lock.sleep(!0) but that doesnt help either.
I add the code to the procedure in the "show some code box"
procedure init_edi_message_line(message_id in number) is
pragma autonomous_transaction;
message_id_ number;
order_no_ varchar2(20);
supplier_no_ varchar2(20);
c08_ varchar2(200);
cursor c1 is
select c08
from jdifs.out_message_line_tab
where message_id = message_id_
and name = 'HEADER';
begin
-- dbms_lock.sleep(10);
message_id_ := message_id;
open c1;
loop
fetch c1
into c08_;
exit when c08_ is not null;
insert into jdifs.jdws_temp_line_tab
values
(message_id_, '2', c08_, '4');
commit;
END LOOP;
close c1;
EXCEPTION
WHEN NO_DATA_FOUND THEN
-- Do something
null;
WHEN OTHERS THEN
null;
end init_edi_message_line;
EDIT:
Hi, no this didnt solve the problem unfortunately,
I will try again to explain as thourougly as possible.
I have a trigger on the table called out_message_line_tab. When a row is created in that table it contains a big number of columns.
the ones that are interesting to me are message_id(which is a sequential number), order_no (P123456), supplier_no(11242), linenumber(1), part_no (F1524).
When the trigger fires data needs to be fetched from that table (and a table "connected to this table" in this case, out_message_tab.
So the trigger is on out_message_line_tab, but it isnt enough to send the values in the trigger to the procedure, since I need some data from the other table as well.
The primary key between the tables out_message_tab and out_message_line_tab is message_id
So my problem is how to do the select from out_message_tab where message_id = message_id(primary key from out_message_line_tab
When I do, it just says no data found. I assume its because it has not been commited yet.
I hope this is clearer.
Your procedure init_edi_message_line() is defined using pragma autonomous_transaction. That means it executes in a completely separate session. Consequently it cannot see any of the uncommitted data in the session which fired the trigger.
If you want init_edi_message_line() to process data from that session your triggers needs to pass everything to the procedure as an argument. However it's not clear exactly what you're doing - is out_message_line_tab the table which owns the trigger? - so I can't guarantee that it will be easy for you to make the necessary changes.
So I am working on adding a last updated time to the database for my app's server. The idea is that it will record the time an update is applied to one of our trips and then the app can send a get request to figure out if it's got all of the correct up to date information.
I've added the column to our table, and provided the service for it all, and finally manage to get a trigger going to update the column every time a change is made to a trip in it's trip table. My problem now comes from the fact that the information that pertains to a trip is stored across a multitude of other tables as well (for instance, there are tables for the routes that make up a trip and the photos that a user can see on the trip, etc...) and if any of that data changes, then the trip's update time also needs to change. I can't for the life of me figure out how to set up the trigger so that when I change some route information, the last updated time for the trip(s) the route belongs to will be updated in it's table.
This is my trigger code as it stands now: it updates the trip table's last updated column when that trip's row is updated.
CREATE OR REPLACE FUNCTION record_update_time() RETURNS TRIGGER AS
$$
BEGIN
NEW.last_updated=now();
RETURN NEW;
END;
$$
LANGUAGE PLPGSQL;
CREATE TRIGGER update_entry_on_entry_change
BEFORE UPDATE ON mydatabase.trip FOR EACH ROW
EXECUTE PROCEDURE record_update_time();
--I used the next two queries just to test that the trigger works. It
--probably doesn't make a difference to you but I'll keep it here for reference
UPDATE mydatabase.trip
SET title='Sample New Title'
WHERE id = 2;
SELECT *
FROM mydatabase.trip
WHERE mydatabase.trip.id < 5;
Now I need it to update when the rows referencing the trip row with a foreign key get updated. Any ideas from someone more experienced with SQL triggers than I?
"mydatabase" is a remarkably unfortunate name for a schema.
The trigger function could look like this:
CREATE OR REPLACE FUNCTION trg_upaft_upd_trip()
RETURNS trigger
LANGUAGE plpgsql AS
$func$
BEGIN
UPDATE mydatabase.trip t -- "mydatabase" = schema name (?!)
SET last_updated = now()
WHERE t.id = NEW.trip_id -- guessing column names
RETURN NULL; -- calling this AFTER UPDATE
END
$func$;
And needs to be used in a trigger on every related table (not on trip itself):
CREATE TRIGGER upaft_upd_trip
AFTER UPDATE ON mydatabase.trip_detail
FOR EACH ROW EXECUTE PROCEDURE trg_upaft_upd_trip();
You also need to cover INSERT and DELETE (and possibly COPY) on all sub-tables ...
This approach has many potential points of failure. As alternative, consider a query or view that computes the latest last_updated from sub-tables dynamically. If you update often this might be the superior approach.
If you rarely UPDATE and SELECT often, your first approach might pay.
I am learning to use triggers in PostgreSQL but run into an issue with this code:
CREATE OR REPLACE FUNCTION checkAdressen() RETURNS TRIGGER AS $$
DECLARE
adrCnt int = 0;
BEGIN
SELECT INTO adrCnt count(*) FROM Adresse
WHERE gehoert_zu = NEW.kundenId;
IF adrCnt < 1 OR adrCnt > 3 THEN
RAISE EXCEPTION 'Customer must have 1 to 3 addresses.';
ELSE
RAISE EXCEPTION 'No exception';
END IF;
END;
$$ LANGUAGE plpgsql;
I create a trigger with this procedure after freshly creating all my tables so they are all empty. However the count(*) function in the above code returns 1.
When I run SELECT count(*) FROM adresse; outside of PL/pgSQL, I get 0.
I tried using the FOUND variable but it is always true.
Even more strangely, when I insert some values into my tables and then delete them again so that they are empty again, the code works as intended and count(*) returns 0.
Also if I leave out the WHERE gehoert_zu = NEW.kundenId, count(*) returns 0 which means I get more results with the WHERE clause than without.
--Edit:
Here is an example of how I use the procedure:
CREATE TABLE kunde (
kundenId int PRIMARY KEY
);
CREATE TABLE adresse (
id int PRIMARY KEY,
gehoert_zu int REFERENCES kunde
);
CREATE CONSTRAINT TRIGGER adressenKonsistenzTrigger AFTER INSERT ON Kunde
DEFERRABLE INITIALLY DEFERRED
FOR EACH ROW
EXECUTE PROCEDURE checkAdressen();
INSERT INTO kunde VALUES (1);
INSERT INTO adresse VALUES (1,1);
It looks like I am getting the DEFERRABLE INITIALLY DEFERRED part wrong. I assumed the trigger would be executed after the first INSERT statement but it happens after the second one, although the inserts are not inside a BEGIN; - COMMIT; - Block.
According to the PostgreSQL Documentation inserts are commited automatically every time if not inside such a block and thus there shouldn't be an entry in adresse when the first INSERT statement is commited.
Can anyone point out my mistake?
--Edit:
The trigger and DEFERRABLE INITIALLY DEFERRED seem to be working all right.
My mistake was to assume that since I am not using a BEGIN-COMMIT-Block each insert would be executed in an own transaction with the trigger being executed afterwards every time.
However even without the BEGIN-COMMIT all inserts get bundled into one transaction and the trigger is executed afterwards.
Given this behaviour, what is the point in using BEGIN-COMMIT?
You need a transaction plus the "DEFERRABLE INITIALLY DEFERRED" because of the chicken and egg problem.
starting with two empty tables:
you cannot insert a single row into the person table, because the it needs at least one address.
you cannot insert a single row into the address table, because the FK constraint needs a corresponding row on the person table to exist
This is why you need to bundle the two inserts into one operation: the transaction. You need the BEGIN+ COMMIT, and the DEFERRABLE allows transient forbidden database states to exists: it causes the check to be evaluated at commit time.
This may seem a bit silly, but the answer is you need to stop deferring the trigger and run it BEFORE the insert. If you run it after the insert, of course there is data in the table.
As far as I can tell this is working as expected.
One further note, you probably dont mean:
RAISE EXCEPTION 'No Exception';
You probably want
RAISE INFO 'No Exception';
Then you can change your settings and run queries in transactions to test that the trigger does what you want it to do. As it is, every insert is going to fail and you have no way to move this into production without editing your procedure.