David Rowley <david.row...@2ndquadrant.com> writes:
> I imagined this would have had a check for volatile functions and some
> user-friendly error message to say partition bounds must be immutable,
> but instead, it does:

> postgres=# create table d_p1 partition of d for values in (Random());
> ERROR:  specified value cannot be cast to type double precision for column "d"
> LINE 1: create table d_p1 partition of d for values in (Random());
>                                                         ^
> DETAIL:  The cast requires a non-immutable conversion.
> HINT:  Try putting the literal value in single quotes.

> For inspiration, maybe you could follow the lead of CREATE INDEX:

> postgres=# create index on d ((random()));
> ERROR:  functions in index expression must be marked IMMUTABLE

Well, that just begs the question: why do these expressions need to
be immutable?  What we really want, I think, is to evaluate them
and reduce them to constants.  After that, it hardly matters whether
the original expression was volatile.  I see absolutely no moral
difference between "for values in (random())" and cases like
this, which works today:

regression=# create table pp(d1 date) partition by range(d1);
regression=# create table cc partition of pp for values from ('today') to 
regression=# \d+ cc
                                   Table "public.cc"
 Column | Type | Collation | Nullable | Default | Storage | Stats target | Descr
 d1     | date |           |          |         | plain   |              | 
Partition of: pp FOR VALUES FROM ('2018-04-10') TO ('2018-04-11')
Partition constraint: ((d1 IS NOT NULL) AND (d1 >= '2018-04-10'::date) AND (d1 <

If we're willing to reduce 'today'::date to a fixed constant,
why not random()?

                        regards, tom lane

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