alamb commented on issue #15363:
URL: https://github.com/apache/datafusion/issues/15363#issuecomment-2758210504
In general, adding Catalog/Schema information to functions makes sense to
me, but I think it would be a non trivial effort
> However, suppose I want to register a custom avg for Duration. In that
case, it means that I need to re-implement the whole avg function because the
new implementation will override the previous one when registered.
Another approach could be to implement your own `avg` function as a wrapper
around `avg` that called into the provided implementation. For example
```rust
/// An average that also supports duration
pub struct AvgWithDuration {
// standard DataFusion average impmenetation
inner: Average
}
/// implement aggregate udf for new average, call
impl AggregateUDFImpl for AvgWithDuration {
...
fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
// handle duration
if arg_types[0] == DataType::Duration {
Ok(DataType::Duration)
}
// otherwise, fall back to inner implementation
self.inner.return_type(arg_types)
}
fn accumulator(&self, acc_args: AccumulatorArgs) -> Result<Box<dyn
Accumulator>> {
// handle duration, with accumulator implemented for Duration
if arg_types[0] == DataType::Duration {
Ok(Box::new(DurationAccumulator(...))
}
// otherwise, fall back to inner implementation
self.inner.return_type(arg_types)
}
...
}
```
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