Trait datafusion::physical_expr::AggregateExpr

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pub trait AggregateExpr: Send + Sync + Debug + PartialEq<dyn Any> {
    // Required methods
    fn as_any(&self) -> &(dyn Any + 'static);
    fn field(&self) -> Result<Field, DataFusionError>;
    fn create_accumulator(
        &self
    ) -> Result<Box<dyn Accumulator, Global>, DataFusionError>;
    fn state_fields(&self) -> Result<Vec<Field, Global>, DataFusionError>;
    fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>, Global>;

    // Provided methods
    fn order_bys(&self) -> Option<&[PhysicalSortExpr]> { ... }
    fn name(&self) -> &str { ... }
    fn row_accumulator_supported(&self) -> bool { ... }
    fn create_row_accumulator(
        &self,
        _start_index: usize
    ) -> Result<Box<dyn RowAccumulator, Global>, DataFusionError> { ... }
    fn reverse_expr(&self) -> Option<Arc<dyn AggregateExpr>> { ... }
    fn create_sliding_accumulator(
        &self
    ) -> Result<Box<dyn Accumulator, Global>, DataFusionError> { ... }
}
Expand description

An aggregate expression that:

  • knows its resulting field
  • knows how to create its accumulator
  • knows its accumulator’s state’s field
  • knows the expressions from whose its accumulator will receive values

Any implementation of this trait also needs to implement the PartialEq<dyn Any> to allows comparing equality between the trait objects.

Required Methods§

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fn as_any(&self) -> &(dyn Any + 'static)

Returns the aggregate expression as Any so that it can be downcast to a specific implementation.

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fn field(&self) -> Result<Field, DataFusionError>

the field of the final result of this aggregation.

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fn create_accumulator( &self ) -> Result<Box<dyn Accumulator, Global>, DataFusionError>

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

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fn state_fields(&self) -> Result<Vec<Field, Global>, DataFusionError>

the fields that encapsulate the Accumulator’s state the number of fields here equals the number of states that the accumulator contains

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fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>, Global>

expressions that are passed to the Accumulator. Single-column aggregations such as sum return a single value, others (e.g. cov) return many.

Provided Methods§

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fn order_bys(&self) -> Option<&[PhysicalSortExpr]>

Order by requirements for the aggregate function By default it is None (there is no requirement) Order-sensitive aggregators, such as FIRST_VALUE(x ORDER BY y) should implement this

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fn name(&self) -> &str

Human readable name such as "MIN(c2)". The default implementation returns placeholder text.

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fn row_accumulator_supported(&self) -> bool

If the aggregate expression is supported by row format

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fn create_row_accumulator( &self, _start_index: usize ) -> Result<Box<dyn RowAccumulator, Global>, DataFusionError>

RowAccumulator to access/update row-based aggregation state in-place. Currently, row accumulator only supports states of fixed-sized type.

We recommend implementing RowAccumulator along with the standard Accumulator, when its state is of fixed size, as RowAccumulator is more memory efficient and CPU-friendly.

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fn reverse_expr(&self) -> Option<Arc<dyn AggregateExpr>>

Construct an expression that calculates the aggregate in reverse. Typically the “reverse” expression is itself (e.g. SUM, COUNT). For aggregates that do not support calculation in reverse, returns None (which is the default value).

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fn create_sliding_accumulator( &self ) -> Result<Box<dyn Accumulator, Global>, DataFusionError>

Creates accumulator implementation that supports retract

Implementors§