Jimexist commented on a change in pull request #403: URL: https://github.com/apache/arrow-datafusion/pull/403#discussion_r642104014
########## File path: datafusion/src/physical_plan/expressions/nth_value.rs ########## @@ -0,0 +1,223 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +//! Defines physical expressions that can evaluated at runtime during query execution + +use crate::error::{DataFusionError, Result}; +use crate::physical_plan::{ + window_functions::BuiltInWindowFunctionExpr, PhysicalExpr, WindowAccumulator, +}; +use crate::scalar::ScalarValue; +use arrow::datatypes::{DataType, Field}; +use std::any::Any; +use std::convert::TryFrom; +use std::sync::Arc; + +/// first_value expression +#[derive(Debug)] +pub struct FirstValue { + name: String, + data_type: DataType, + expr: Arc<dyn PhysicalExpr>, +} + +impl FirstValue { + /// Create a new FIRST_VALUE window aggregate function + pub fn new(expr: Arc<dyn PhysicalExpr>, name: String, data_type: DataType) -> Self { + Self { + name, + data_type, + expr, + } + } +} + +impl BuiltInWindowFunctionExpr for FirstValue { + /// Return a reference to Any that can be used for downcasting + fn as_any(&self) -> &dyn Any { + self + } + + fn field(&self) -> Result<Field> { + let nullable = true; + Ok(Field::new(&self.name, self.data_type.clone(), nullable)) + } + + fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>> { + vec![self.expr.clone()] + } + + fn name(&self) -> &str { + &self.name + } + + fn create_accumulator(&self) -> Result<Box<dyn WindowAccumulator>> { + Ok(Box::new(NthValueAccumulator::try_new( + 1, + self.data_type.clone(), + )?)) + } +} + +// sql values start with 1, so we can use 0 to indicate the special last value behavior +const SPECIAL_SIZE_VALUE_FOR_LAST: u32 = 0; + +/// last_value expression +#[derive(Debug)] +pub struct LastValue { + name: String, + data_type: DataType, + expr: Arc<dyn PhysicalExpr>, +} + +impl LastValue { + /// Create a new FIRST_VALUE window aggregate function + pub fn new(expr: Arc<dyn PhysicalExpr>, name: String, data_type: DataType) -> Self { + Self { + name, + data_type, + expr, + } + } +} + +impl BuiltInWindowFunctionExpr for LastValue { + /// Return a reference to Any that can be used for downcasting + fn as_any(&self) -> &dyn Any { + self + } + + fn field(&self) -> Result<Field> { + let nullable = true; + Ok(Field::new(&self.name, self.data_type.clone(), nullable)) + } + + fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>> { + vec![self.expr.clone()] + } + + fn name(&self) -> &str { + &self.name + } + + fn create_accumulator(&self) -> Result<Box<dyn WindowAccumulator>> { + Ok(Box::new(NthValueAccumulator::try_new( + SPECIAL_SIZE_VALUE_FOR_LAST, + self.data_type.clone(), + )?)) + } +} + +/// nth_value expression +#[derive(Debug)] +pub struct NthValue { + name: String, + n: u32, + data_type: DataType, + expr: Arc<dyn PhysicalExpr>, +} + +impl NthValue { + /// Create a new NTH_VALUE window aggregate function + pub fn try_new( + expr: Arc<dyn PhysicalExpr>, + name: String, + n: u32, + data_type: DataType, + ) -> Result<Self> { + if n == SPECIAL_SIZE_VALUE_FOR_LAST { + Err(DataFusionError::Execution( + "nth_value expect n to be > 0".to_owned(), + )) + } else { + Ok(Self { + name, + n, + data_type, + expr, + }) + } + } +} + +impl BuiltInWindowFunctionExpr for NthValue { + /// Return a reference to Any that can be used for downcasting + fn as_any(&self) -> &dyn Any { + self + } + + fn field(&self) -> Result<Field> { + let nullable = true; + Ok(Field::new(&self.name, self.data_type.clone(), nullable)) + } + + fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>> { + vec![self.expr.clone()] + } + + fn name(&self) -> &str { + &self.name + } + + fn create_accumulator(&self) -> Result<Box<dyn WindowAccumulator>> { + Ok(Box::new(NthValueAccumulator::try_new( + self.n, + self.data_type.clone(), + )?)) + } +} + +#[derive(Debug)] +struct NthValueAccumulator { + // n the target nth_value, however we'll reuse it for last_value acc, so when n == 0 it specifically Review comment: to address later: https://github.com/apache/arrow-datafusion/issues/448 -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
