Re: Same expression more than once in partition key

On Fri, 23 Jun 2017 09:54:17 -0400
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp> writes:
> > When we create a range partitioned table, we cannot use
> > a column more than once in the partition key.
>
> > postgres=# create table t (i int) partition by range(i,i);
> > ERROR: column "i" appears more than once in partition key
>
> AFAIK, that's just a simple test for obvious mistakes; it's not a
> property that's essential for correctness.

Thanks. This is what I want to know.

>
> > However, I can use same expression more than once in partition key.
>
> ... and so, I can't get excited about extending it to expressions.
> Where would you stop --- for example, are i and (i) equal? What
> about (i) and (case when true then i else j end)? In principle,
> the system could recognize both those identities, but it seems
> silly to expend code on it just for nagware purposes.
>

Agreed.

> regards, tom lane

--
Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>