Re: Triggers on columns

Robert Haas wrote:
> On Wed, Sep 2, 2009 at 9:52 PM, Itagaki
> Takahiro<itagaki.takahiro@oss.ntt.co.jp> wrote:
>   
>> Here is a patch to implement "Support triggers on columns" in our ToDo list.
>>
>> The syntax is:
>>    CREATE TRIGGER name
>>        BEFORE UPDATE OF col1, col12, ...
>>        ON tbl FOR EACH ROW EXECUTE PROCEDURE func();
>>
>> I consulted the previous work following:
>>    Column-level triggers (From: Greg Sabino Mullane, Date: 2005-07-04)
>>    http://archives.postgresql.org/pgsql-patches/2005-07/msg00107.php
>> and completed some under-construction parts.
>>
>> It's still arguable that we should add dependencies from column
>> triggers to referenced columns. In the present patch, dropeed
>> columns are just ignored and always considered as not-modified.
>> Please grep with "TODO: (TRIGGER)" to check the issue.
>>
>> Comments welcome.
>>     
>
> Wow, so I wouldn't have to do this any more?
>
> IF (TG_OP = 'UPDATE') THEN
>     IF (OLD.foo IS NOT DISTINCT FROM NEW.foo AND OLD.bar IS NOT
> DISTINCT FROM NEW.bar
>          AND OLD.baz IS NOT DISTINCT FROM NEW.baz) THEN
>         RETURN NULL;
>     END IF;
> END IF;
>
> Apart from any possible gain in efficiency, the sheer savings in
> typing sound quite awesome.
>
>
>   

You could make it nicer with something like:
  row(new.foo,new.bar,new.baz) is distinct from 
row(old.foo,old.bar,old.baz)

couldn't you?

I'm actually having trouble thinking of a case where I'd find this 
feature very useful.

cheers

andrew