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Re: Trigger function to know which fields are being updated

From: Jeff Eckermann <jeff_eckermann(at)yahoo(dot)com>
To: Bernard Cheung <cheungsw(at)hotmail(dot)com>, pgsql-sql(at)postgresql(dot)org
Subject: Re: Trigger function to know which fields are being updated
Date: 2004-05-11 13:59:03
Message-ID: 20040511135903.69008.qmail@web20804.mail.yahoo.com (view raw or flat)
Thread:
Lists: pgsql-sql
--- Bernard Cheung <cheungsw(at)hotmail(dot)com> wrote:
> Thank you, but my intension is to check whether the
> user supplies NAME when 
> updating the record.
> 
> For example the trigger shall allow statement 1 and
> block statement 2:
> 
> 1. UPDATE COMPANY SET NAME = 'ABC', ADDRESS = '123
> Drive' WHERE COMPANY_ID = 
> 1;
> 
> 2. UPDATE COMPANY SET ADDRESS = '123 Drive' WHERE
> COMPANY_ID = 1;
> 
> I want the trigger to ensure that the user must
> provide value for NAME when 
> updating this record.

In case 2 above, the updated record will keep the same
"name" value that it had previously.  The logic that
you need to use will depend on precisely what you want
to happen.  For example, if you expect that the name
must change, then you can test "NEW.NAME = OLD.NAME". 
But if the name is not changing, this will not tell
you anything, even if the user is in fact supplying
the name.

Depending on what rules you want to enforce, you may
be better off doing the checking in your application.

> 
> >From: Jeff Eckermann <jeff_eckermann(at)yahoo(dot)com>
> >To: Bernard Cheung <cheungsw(at)hotmail(dot)com>,
> pgsql-sql(at)postgresql(dot)org
> >Subject: Re: [SQL] Trigger function to know which
> fields are being updated
> >Date: Mon, 10 May 2004 14:38:56 -0700 (PDT)
> >
> >
> >--- Bernard Cheung <cheungsw(at)hotmail(dot)com> wrote:
> > > I am writing a trigger function. How can I know
> > > which fields are being
> > > updated in the PL/SQL function?
> > >
> > > For example I have a table here:
> > >
> > >
> > > CREATE TABLE COMPANY (
> > >   COMPANY_ID VARCHAR(10) NOT NULL,
> > >   NAME VARCHAR(30),
> > >   ADDRESS VARCHAR(30));
> > >
> > > I want to write a trigger to block all update
> > > statements without updating
> > > NAME. I tried the following code block and it
> > > doesn't work:
> > >
> > >
> > >   IF TG_OP = ''UPDATE'' THEN
> > >      IF NEW.NAME IS NULL THEN
> > >         RAISE NOTICE ''Field NAME must be
> > > provided!'';
> > >      END IF;
> > >   END IF;
> >
> >That should work.  Perhaps "name" is not actually
> >null, but rather an empty string?  In that case,
> your
> >test needs to be: "IF NEW.NAME IS NULL OR NEW.NAME
> =
> >'''' THEN..."
> >
> > >
> > > Are there any functions like the Oracle's
> UPDATING()
> > > predicate?
> > >
> > > Bernard Cheung
> > >
> > > ---------------------------(end of
> > > broadcast)---------------------------
> > > TIP 1: subscribe and unsubscribe commands go to
> >majordomo(at)postgresql(dot)org
> 
>
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