built_in_window_function_expr.rs

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use super::partition_evaluator::PartitionEvaluator;
use crate::PhysicalExpr;
use arrow::array::ArrayRef;
use arrow::datatypes::Field;
use arrow::record_batch::RecordBatch;
use datafusion_common::Result;
use std::any::Any;
use std::sync::Arc;

/// A window expression that is a built-in window function.
///
/// Note that unlike aggregation based window functions, built-in window functions normally ignore
/// window frame spec, with the exception of first_value, last_value, and nth_value.
pub trait BuiltInWindowFunctionExpr: Send + Sync + std::fmt::Debug {
    /// Returns the aggregate expression as [`Any`](std::any::Any) so that it can be
    /// downcast to a specific implementation.
    fn as_any(&self) -> &dyn Any;

    /// the field of the final result of this aggregation.
    fn field(&self) -> Result<Field>;

    /// expressions that are passed to the Accumulator.
    /// Single-column aggregations such as `sum` return a single value, others (e.g. `cov`) return many.
    fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>>;

    /// Human readable name such as `"MIN(c2)"` or `"RANK()"`. The default
    /// implementation returns placeholder text.
    fn name(&self) -> &str {
        "BuiltInWindowFunctionExpr: default name"
    }

    /// Evaluate window function arguments against the batch and return
    /// an array ref. Typically, the resulting vector is a single element vector.
    fn evaluate_args(&self, batch: &RecordBatch) -> Result<Vec<ArrayRef>> {
        self.expressions()
            .iter()
            .map(|e| e.evaluate(batch))
            .map(|r| r.map(|v| v.into_array(batch.num_rows())))
            .collect()
    }

    /// Create built-in window evaluator with a batch
    fn create_evaluator(&self) -> Result<Box<dyn PartitionEvaluator>>;

    /// Construct Reverse Expression that produces the same result
    /// on a reversed window.  For example `lead(10)` --> `lag(10)`
    fn reverse_expr(&self) -> Option<Arc<dyn BuiltInWindowFunctionExpr>> {
        None
    }

    fn supports_bounded_execution(&self) -> bool {
        false
    }

    fn uses_window_frame(&self) -> bool {
        false
    }
}