Jimexist commented on a change in pull request #375:
URL: https://github.com/apache/arrow-datafusion/pull/375#discussion_r638394414
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File path: datafusion/src/physical_plan/mod.rs
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@@ -457,10 +457,41 @@ pub trait WindowExpr: Send + Sync + Debug {
fn name(&self) -> &str {
"WindowExpr: default name"
}
+
+ /// the accumulator used to accumulate values from the expressions.
+ /// the accumulator expects the same number of arguments as `expressions`
and must
+ /// return states with the same description as `state_fields`
+ fn create_accumulator(&self) -> Result<Box<dyn WindowAccumulator>>;
+
+ /// expressions that are passed to the WindowAccumulator.
+ /// Single-column aggregations such as `sum` return a single value, others
(e.g. `cov`) return many.
+ fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>>;
+}
+
+/// A window expression that is a built-in window function
+pub trait BuiltInWindowFunctionExpr: Send + Sync + Debug {
Review comment:
I've moved `BuiltInWindowFunctionExpr` into `window_functions.rs` where
it's more appropriate.
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