Tom Lane <t...@sss.pgh.pa.us> wrote:
> Itagaki Takahiro <itagaki.takah...@oss.ntt.co.jp> writes:
> > I think there is a benefit to provide WHEN cluase at least
> > for compatibility with other DBMSs, even through we can move
> > the expressions into the body of trigger functions.
>
> This seems to me to be a lot of code to accomplish nothing useful.
> It will always be the case that any nontrivial logic has to be done
> inside the trigger. And the compatibility argument is entirely
> pointless given the lack of compatibility in the trigger function
> itself.
I see that WHEN cluase is not always needed,
but I think there are several benefits to have it:
* WHEN cluase is in SQL standard.
* We could recheck trigger conditions when NEW tuple is modified.
(not yet implemented in the patch, though)
http://archives.postgresql.org/pgsql-hackers/2009-09/msg00286.php
* As for compatibility, it is easy for typical users to move trigger
bodies into a function, but they don't like to merge the condition
and the bodies into a function in my experience.
* As for performance, I don't have any evidence. But there was a
discussion about benefits of writing partitioning trigger function
with C instead of PL/pgSQL. He said pgplsql is slow.
http://archives.postgresql.org/pgsql-hackers/2008-12/msg01221.php
Also, to separate trigger bodies and conditions are useful when we
write triggers in C because we don't have to recomplie the code.
Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center
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