From: Wolfe Whalen <wolfe@quios.net>
To: Kaleeswaran Velu <v_kalees@yahoo.com>
Cc: Postgres SQL List <pgsql-sql@postgresql.org>
Subject: Re: Postgres trigger issue with update statement in it.
Date: Thu, 04 Apr 2013 00:28:26 -0700
Message-ID: <1365060506.15519.140661213164229.7F345F5D@webmail.messagingengine.com> (raw)
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Hi Kaleeswaran,
We're glad to have you on the mailing list. I don't know enough about
your trigger function to know exactly where it's going wrong, but I
threw together a quick example that has an insert trigger on a child
table that updates a row on the parent table. I'm hoping this might
help. If it doesn't help, maybe you could give us a little more
information about your function or tables. I'd be happy to help in any
way that I can.
CREATE TABLE survey_records (
name varchar(100),
obsoleted timestamp DEFAULT NULL
);
CREATE TABLE geo_surveys (
measurement integer
) INHERITS (survey_records);
CREATE OR REPLACE FUNCTION obsolete_old_surveys() RETURNS trigger AS $$
BEGIN
UPDATE survey_records SET obsoleted = clock_timestamp()
WHERE survey_records.name = NEW.name AND survey_records.obsoleted
IS NULL;
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER obsolete_old_surveys_tr
BEFORE INSERT ON geo_surveys
FOR EACH ROW EXECUTE PROCEDURE obsolete_old_surveys();
INSERT INTO geo_surveys (name, measurement) VALUES ('Carbon Dioxide',
5);
INSERT INTO geo_surveys (name, measurement) VALUES ('Carbon Dioxide',
10);
INSERT INTO geo_surveys (name, measurement) VALUES ('Carbon Dioxide',
93);
You'd wind up with something like this:
SELECT * FROM survey_records;
name | obsoleted
----------------+----------------------------
Carbon Dioxide | 2013-04-03 23:59:44.228225
Carbon Dioxide | 2013-04-03 23:59:53.66243
Carbon Dioxide |
(3 rows)
SELECT * FROM geo_surveys;
name | obsoleted | measurement
----------------+----------------------------+-------------
Carbon Dioxide | 2013-04-03 23:59:44.228225 | 5
Carbon Dioxide | 2013-04-03 23:59:53.66243 | 10
Carbon Dioxide | | 93
(3 rows)
The parent survey_records is actually updating the child table rows
when you do an update. Parent tables can almost seem like a view in
that respect. You would have to be a bit careful if you're going to
have an update trigger on a child that updated the parent table. It's
easy to wind up with a loop like this:
Child: Update row 1 -> Trigger function -> Update Row 1 on parent
->Parent: Let's see... Row 1 is contained in this child table, so
let's update it there.
->Child: Update row 1 -> Trigger function -> Update Row 1 on parent
->Parent: Let's see... Row 1 is contained in this child table, so
let's update it there.
... etc etc.
Best Regards,
Wolfe
--
Wolfe Whalen
wolfe@quios.net
On Wed, Apr 3, 2013, at 09:08 PM, Kaleeswaran Velu wrote:
Hello Friends,
I am new to Postgres DB. Recently installed Postgres 9.2.
Facing an issue with very simple trigger, tried to resolve myself by
reading documents or google search but no luck.
I have a table A(parent) and table B (child). There is a BEFORE INSERT
OR UPDATE trigger attached in table B. This trigger has a update
statement in it. This update statement should update a respective
record in table A when ever there is any insert/update happen in table
B. The issue here is where ever I insert/update record in table B,
getting an error as below :
********** Error **********
ERROR: cannot begin/end transactions in PL/pgSQL
SQL state: 0A000
Hint: Use a BEGIN block with an EXCEPTION clause instead.
Context: PL/pgSQL function func_update_payment() line 53 at SQL
statement
Line no 53 in the above error message is an update statement. If I
comment out the update statement, trigger works fine.
Can anyone shed some lights on this? Your help is appreciated.
Thanks and Regards
Kaleeswaran Velu
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Cc: wolfe@quios.net, v_kalees@yahoo.com
Subject: Re: Postgres trigger issue with update statement in it.
In-Reply-To: <1365060506.15519.140661213164229.7F345F5D@webmail.messagingengine.com>
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