Jimexist commented on a change in pull request #334: URL: https://github.com/apache/arrow-datafusion/pull/334#discussion_r636212671
########## File path: datafusion/src/physical_plan/window_functions.rs ########## @@ -0,0 +1,149 @@ +// 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. + +//! Window functions provide the ability to perform calculations across +//! sets of rows that are related to the current query row. +//! +//! see also https://www.postgresql.org/docs/current/functions-window.html + +use crate::error::{DataFusionError, Result}; +use crate::physical_plan::{ + aggregates, aggregates::AggregateFunction, functions::Signature, + type_coercion::data_types, +}; +use arrow::datatypes::DataType; +use std::{fmt, str::FromStr}; + +/// WindowFunction +#[derive(Debug, Clone, PartialEq, Eq)] +pub enum WindowFunction { + /// window function that leverages an aggregate function + AggregateFunction(AggregateFunction), + /// window function that leverages a built-in window function + BuiltInWindowFunction(BuiltInWindowFunction), +} + +impl FromStr for WindowFunction { + type Err = DataFusionError; + fn from_str(name: &str) -> Result<WindowFunction> { + if let Ok(aggregate) = AggregateFunction::from_str(name) { + Ok(WindowFunction::AggregateFunction(aggregate)) + } else if let Ok(built_in_function) = BuiltInWindowFunction::from_str(name) { + Ok(WindowFunction::BuiltInWindowFunction(built_in_function)) + } else { + Err(DataFusionError::Plan(format!( + "There is no built-in function named {}", + name + ))) + } + } +} + +impl fmt::Display for BuiltInWindowFunction { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + // uppercase of the debug. + write!(f, "{}", format!("{:?}", self).to_uppercase()) + } +} + +impl fmt::Display for WindowFunction { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + match self { + WindowFunction::AggregateFunction(fun) => fun.fmt(f), + WindowFunction::BuiltInWindowFunction(fun) => fun.fmt(f), + } + } +} + +/// An aggregate function that is part of a built-in window function +#[derive(Debug, Clone, PartialEq, Eq)] +pub enum BuiltInWindowFunction { + /// row number + RowNumber, + /// rank + Rank, + /// dense rank + DenseRank, + /// lag + Lag, + /// lead + Lead, + /// first value + FirstValue, + /// last value + LastValue, +} + +impl FromStr for BuiltInWindowFunction { + type Err = DataFusionError; + fn from_str(name: &str) -> Result<BuiltInWindowFunction> { Review comment: done -- 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
