discord9 commented on code in PR #15854:
URL: https://github.com/apache/datafusion/pull/15854#discussion_r2067801065
##########
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:
> To further clarify, at the SQL/Relational level
>
> ```sql
> SELECT null::text[], array[]::text[]
>
> text | array
> ---- | --
> null | {}
> ```
>
> we can distinguish between casting a null literal to a compound type, and
the empty version of that compound type.
>
> [dbfiddle](https://www.db-fiddle.com/f/cH7Hwk6mHnm3rgy7wXG4Yq/47)
Oh I didn't realize `is_null` do extra things other than matches with
`ScalarValue::Null`, I shall only match `ScalarValue::Null` then
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