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Re: [NOVICE] trigger to access only the last transaction - Mailing list pgsql-sql

From s d
Subject Re: [NOVICE] trigger to access only the last transaction
Date
Msg-id CAKyoTgZkSfCKe2aC7Ji=eKrZMxei0_JoDnY3LUL5RWg=FWVUPg@mail.gmail.com
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In response to trigger to access only the last transaction  (avpro avpro <avprowebeden@gmail.com>)
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Hi,

Do as Frank said! It will solve your problem.
Forget your task for a minute and check your command:

update table2
SET 
manualdueat = null,
FROM table1, 
where table1.idtask = table2.idtask;

Works as a charm, and updates all record in table2 which have an matching counterpart in table1. :)

In per row trigger procedures you have access to the old and new version of currently processed record trough the NEW and OLD record variables. In your trigger procedure you have to update only the record in table2 where table2.idtask=new.idtask.
And just for fun in BEFORE triggers you can also modify the NEW record and with returning  NEW modify the whole result of the DML command which activated the trigger, or even refuse it completely with returning NULL; 

Regards,
Sándor Daku


On 8 March 2015 at 23:01, avpro avpro <avprowebeden@gmail.com> wrote:
hi all,

i have two tables with several columns:
table1
idtaskhistory
performedat
...
idtask

and

table2
idtask,
manualdueat
.....


i created a trigger that does the following:

CREATE TRIGGER del1
  AFTER INSERT
  ON table1
  FOR EACH ROW
  EXECUTE PROCEDURE taskdel;

taskdel:
CREATE OR REPLACE FUNCTION taskdel()
  RETURNS trigger AS
$BODY$begin
update table2
SET
manualdueat = null,
FROM table1,
where table1.idtask = table2.idtask;
return new;
END$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;
ALTER FUNCTION taskdel()
  OWNER TO user1;

my idea was to have the info from column "manualdueat" deleted after the table1 has been updated. the problem i face is that all columns from table2 will be deleted, not only my last entry where the insert has been done (I was thinking that table1.idtask = table2.idtask will work, but isn't); my question to you would be how to access only the last insert id in table1 and make this trigger working. or do you have another walk arround?
I'm using psql 9.4 on a windows system

thank you for your ideas,
John

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