Blizzara commented on code in PR #15854:
URL: https://github.com/apache/datafusion/pull/15854#discussion_r2068664824
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datafusion/substrait/src/logical_plan/producer.rs:
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@@ -1590,6 +1590,21 @@ pub fn from_cast(
schema: &DFSchemaRef,
) -> Result<Expression> {
let Cast { expr, data_type } = cast;
+ // since substrait Null must be typed, so if we see a cast(null, dt), we
make it a typed null
+ if let Expr::Literal(lit) = expr.as_ref() {
+ if lit.is_null() {
Review Comment:
@vbarua re
> But for compound types I'm not sure if it does the right thing for the
fold you're introducing:
> because I don't think that it make sense to flatten empty compound types.
If I understand how this would work, something like
There is a comment in the code of "is_null" before those:
> // arr.len() should be 1 for a list scalar, but we don't seem
to
> // enforce that anywhere, so we still check against array
length.
I haven't validated if that is correct, but I guess the idea is that a
SV:List is null if the _outer, "one-row" list itself_ is null. If that list is
not null, then the inner list can be empty. So an empty compound type would
have first the `arr` with `arr.len() = 1, and `arr.null_count() = 0`, passing
the check; then arr.values(0) would be another list which can have its own
length and null count (where e.g. both would then be zero for an empty list).
So unless I misunderstood what you meant, or there's some bug that I'm not
aware of / or a difference in the behavior to what I think it is, I do believe
the earlier code was also correct. However the change to only deal with SV:Null
seems good to me as well.
(I do find it annoying how complicated the compound types for SV are to
understand. Why is SV::List a single-row ListArray instead of just a
Vec<ScalarValue> ? But maybe there's a reason, and in any case changing that is
probably too much of a hassle now, and totally outside the scope of this PR 😄 )
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