Re: [HACKERS] Same expression more than once in partition key

Yugo Nagata <nagata@sraoss.co.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.

> 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.
        regards, tom lane