Re: Boolean partitions syntax

At Wed, 11 Apr 2018 11:27:17 +0900, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote in <1810b14f-3cd7-aff5-8358-c225c0231ee9(at)lab(dot)ntt(dot)co(dot)jp>
> On 2018/04/11 10:44, Tom Lane wrote:
> > Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> writes:
> >> At least partition bound *must* be a constant. Any expression
> >> that can be reduced to a constant at parse time ought to be
> >> accepted but must not be accepted if not.
> >
> > My point is that *any* expression can be reduced to a constant,
> > we just have to do so.

Agreed in that sense. What was in my mind was something like
column reference, random() falls into reducible category of
course.

# I regard the change in gram.y is regarded as acceptable as a
# direction, so I'll continue to working on this.

> Currently transformPartitionBoundValue() applies eval_const_expressions()
> by way of calling expression_planner(). However passing to it, say, an
> expression representing random() is unable to reduce it to a Const because
> simplify_function/evaluate_function won't compute a mutable function like
> random(). So, that currently results in an error like this (note that
> this is after applying Horiguchi-san's latest patch that enables
> specifying random() as a partition bound in the first place):
>
> create table foo_part partition of foo for values in ((random())::int);
> ERROR: specified value cannot be cast to type integer for column "a"
> LINE 1: ...table foo_random partition of foo for values in ((random()):...
> ^
> DETAIL: The cast requires a non-immutable conversion.
> HINT: Try putting the literal value in single quotes.
>
> The error is output after the following if check in
> transformPartitionBoundValue fails:
>
> /* Fail if we don't have a constant (i.e., non-immutable coercion) */
> if (!IsA(value, Const))
>
> I think what Tom is proposing here, instead of bailing out upon
> eval_const_expressions() failing to simplify the input expression to a
> Const, is to *invoke the executor* to evaluate the expression, like the
> optimizer does in evaluate_expr, and cook up a Const with whatever comes
> out to store it into the catalog (that is, in relpartbound).

Yes. In the attached I used evaluate_expr by making it non-static
function. a_expr used instead of partbound_datum is changed to
u_expr, which is the same with range bounds.

> =# create table c1 partition of p for values in (random() * 100);
> CREATE TABLE
> =# \d c1
...
> Partition of: p FOR VALUES IN (97)

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center