Re: Triggers on columns

From: Itagaki Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Triggers on columns
Date: 2009-09-07 02:20:06
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Here is a updated version of column-trigger patch.

Changes from the previous patch:
* Add dependency of columns with recordDependencyOn().
Regression tests are also adjusted.
* Recheck columns if NEW values are modified, but each trigger
will be firec only one per row.

Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:
> The SQL standard specifies that a trigger is fired if the column is
> mentioned in the UPDATE statement, independent of whether the value is
> actually changed through the update.

We are discussing how to determine modified columns
(UPDATE-target vs. changes of actual values), but in the patch
I used value-based checking. The reasons are:
1. Other triggers could modify referred columns even if the columns
are not specifed in UPDATE-target.
2. IMHO, almost users don't expect their triggers are not called
if the actual values are not modified.
3. Restriction of implementation; We don't have RTE in trigger
routine for now. The current patch doesn't modify codes a lot.

Comments welcome.

ITAGAKI Takahiro
NTT Open Source Software Center

Attachment Content-Type Size
column-trigger-20090907.patch application/octet-stream 35.4 KB

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