Re: Postgres trigger issue with update statement in it.

Hi Mr. Wolfe,
Thanks for your response. I have received e-mails from several others. Thanks for everyone and appreciate your help.

Mr. Wolfe sent a sample code. I took that as the base and debugged my code and identified the issue. Now my code is working fine. I have identified the real culprit.

Earlier my trigger was as like 

CREATE OR REPLACE FUNCTION fun_update_payments() RETURNS TRIGGER AS $trg_update_payments$
DECLARE
BEGIN

    UPDATE jl
    SET jl.outstanding = jl.outstanding - new.Principle_Amount
    WHERE jl.jl_id=new.jl_id;
        

    RETURN new;
    
    EXCEPTION WHEN OTHERS THEN
       ROLLBACK;
       RAISE NOTICE 'fun_update_payment() Failed...';
   
END
$trg_update_payments$ LANGUAGE plpgsql;

After debugging I found my Update statement is wrong, I should not have prefix as <table_name.> (Oracle accepts this.). I then changed that to as below and stared working.

    UPDATE jl
    SET outstanding = outstanding - new.Principle_Amount
    WHERE jl_id=new.jl_id;
 
Somehow Postgres is not capturing this at the compilation time. 
But at run time, instead of throwing syntax error, it was trowing some transactional error as "ERROR: cannot begin/end transactions in PL/pgSQL". The reason for that is the EXCEPTION  block that I had at the end.

I then removed below block from the trigger, then it was throwing expected syntax error at run time. 
    EXCEPTION WHEN OTHERS THEN
       ROLLBACK;
       RAISE NOTICE 'fun_update_payment() Failed...';

However it works now. Again thanks to Mr. Wolfe.

Thanks and Regards
Kaleeswaran Velu

________________________________
From: Wolfe Whalen <wolfe(at)quios(dot)net>
To: Kaleeswaran Velu <v_kalees(at)yahoo(dot)com>
Cc: Postgres SQL List <pgsql-sql(at)postgresql(dot)org>
Sent: Thursday, April 4, 2013 12:58 PM
Subject: Re: [SQL] Postgres trigger issue with update statement in it.

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(at)quios(dot)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
>