duongcongtoai commented on code in PR #10429:
URL: https://github.com/apache/datafusion/pull/10429#discussion_r1608935540
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datafusion/expr/src/expr_schema.rs:
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@@ -123,7 +123,8 @@ impl ExprSchemable for Expr {
Ok(field.data_type().clone())
}
DataType::Struct(_) => {
- not_impl_err!("unnest() does not support struct yet")
+ // TODO: this is not correct, because unnest(struct)
wll result into multiple data_type
Review Comment:
if we returns error here, the error will stop the query plan from continue.
Initially unnest comes into projection step as an Expr here:
https://github.com/apache/datafusion/blob/d58bae487329b7a7078429f083bffc611f42c8c7/datafusion/expr/src/utils.rs#L734,
where it check data types of each expr, then later on we call
[try_process_unnest](https://github.com/apache/datafusion/blob/ae4b3a0f8366ab18be5ef5cfa2b3cc3aca12baf1/datafusion/sql/src/select.rs#L226)
to do the transformation from unnest(struct) -> struct.field1, struct.field 2
...
I think unnest is the only expr so far that represent a set of fields
instead of singular value here, so i'm thinking of adding an extra check at
this function
https://github.com/apache/datafusion/blob/d58bae487329b7a7078429f083bffc611f42c8c7/datafusion/expr/src/utils.rs#L734
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