| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Greg Stark <stark(at)enterprisedb(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Yoshiyuki Asaba <y-asaba(at)sraoss(dot)co(dot)jp>, Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Common Table Expressions applied; some issues remain |
| Date: | 2009-05-27 11:20:01 |
| Message-ID: | 4A1D21E1.1000309@enterprisedb.com |
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| Lists: | pgsql-hackers |
Greg Stark wrote:
> On Wed, May 27, 2009 at 12:47 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I'm not too thrilled about that solution because it still eliminates
>> predictability of execution of volatile functions.
>
> How so? It means the volatile function might only be executed for the
> matching rows but the rows will still have the same value for the same
> rows for all references to the CTE which seems like the key property
> to me.
A volatile function could have side-effects, ie. insert rows to another
table. I would not recommend a design that relies on such behavior, but
it should be predictable how often the volatile function is run if you
do that.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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