timsaucer commented on issue #6747:
URL: https://github.com/apache/datafusion/issues/6747#issuecomment-2236257604
I've started looking at this and coming up against one blocker that prevents
just following the exact pattern.
My first thought was to implement a trait like
```
pub trait WindowExt {
fn order_by(self, order_by: Vec<Expr>) -> WindowBuilder;
fn partition_by(self, partitions: Vec<Expr>) -> WindowBuilder;
fn window_frame(self, window_frame: WindowFrame) -> WindowBuilder;
fn null_treatment(self, null_treatment: NullTreatment) -> WindowBuilder;
}
```
The problem with this is that we would have two traits implemented on `Expr`
that have two identical function names, `order_by` and `null_treatment`. I
*could* give them different names, but that isn't a great user experience. Plus
there's the fact that all aggregate functions can be used as window functions.
My current thinking is that instead of doing this, I should rename
`AggregateExt` to something like `ExprExt`. This trait would have something like
```
pub trait ExprExt {
fn order_by(self, order_by: Vec<Expr>) -> ExprBuilder;
fn filter(self, filter: Expr) -> ExprBuilder;
fn distinct(self) -> ExprBuilder;
fn partition_by(self, partitions: Vec<Expr>) -> ExprBuilder;
fn window_frame(self, window_frame: WindowFrame) -> ExprBuilder;
fn null_treatment(self, null_treatment: NullTreatment) -> ExprBuilder;
}
```
Then the `ExprBuilder` would do something like
```
pub struct ExprBuilder {
expr_data: ExprBuilderData,
order_by: Option<Vec<Expr>>,
filter: Option<Expr>,
distinct: bool,
null_treatment: Option<NullTreatment>,
}
```
And finally
```
enum ExprBuilderData {
AggregateBuilderData(AggregateFunction),
WindowBuilderData(WindowFunction),
CaseBuilderData(Case),
None,
}
```
I haven't dug too much deeper into it, but these are my initial design
ideas. @jayzhan211 and @alamb what do you think?
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