jackwener opened a new issue, #6681:
URL: https://github.com/apache/arrow-datafusion/issues/6681
### Is your feature request related to a problem or challenge?
In the current optimization of Datafusion, we often use Expr::Alias
instances for purposes:
1. allow the parent plan to correctly access the corresponding column.
2. ensure that the column name remains unchanged.
3. prevent changes to the schema.
4.
However, there is a vulnerability in this process. When an alias contains a
qualifier, the schema cannot remain unchanged.
Here's an example:
Original column: t.c1 (field: qualifier: t, name: c1)
New column: c2 as t.c1 (its field will be: field: qualifier: None, name:
t.c1)
### Describe the solution you'd like
I try to match Expr::Alias and handle it in `to_field()`.
such as
```rust
fn to_field(&self, input_schema: &DFSchema) -> Result<DFField> {
match self {
Expr::Alias(e, alias) if alias.contains('.') => {
let index = alias.rfind('.').unwrap();
let qualifier = alias[..index].to_string();
let name = alias[index + 1..].to_string();
Ok(DFField::new(
Some(qualifier),
&name,
e.get_type(input_schema)?,
e.nullable(input_schema)?,
))
}
Expr::Column(c) => Ok(DFField::new(
c.relation.clone(),
&c.name,
self.get_type(input_schema)?,
self.nullable(input_schema)?,
)),
```
but I failed, because `alias` can be complex, we hard to parse it and
separate qualifier and name.
such as above code will fail in expr like `Cast(t1.a as int)`
So, I propose to add a `schema` in Expr::Alias, so we will get schema of
Expr::Alias directly
### Describe alternatives you've considered
_No response_
### Additional context
_No response_
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