drusso commented on a change in pull request #8222: URL: https://github.com/apache/arrow/pull/8222#discussion_r501684962
########## File path: rust/datafusion/src/physical_plan/distinct_expressions.rs ########## @@ -0,0 +1,203 @@ +// 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. + +//! Implementations for DISTINCT expressions, e.g. `COUNT(DISTINCT c)` + +use std::cell::RefCell; +use std::convert::TryFrom; +use std::fmt::Debug; +use std::hash::Hash; +use std::rc::Rc; +use std::sync::Arc; + +use arrow::array::ArrayRef; +use arrow::array::ListArray; +use arrow::datatypes::{DataType, Field}; + +use fnv::FnvHashSet; + +use crate::error::{ExecutionError, Result}; +use crate::physical_plan::group_scalar::GroupByScalar; +use crate::physical_plan::{Accumulator, AggregateExpr, PhysicalExpr}; +use crate::scalar::ScalarValue; + +#[derive(Debug, PartialEq, Eq, Hash, Clone)] +struct DistinctScalarValues(Vec<GroupByScalar>); + +fn format_state_name(name: &str, state_name: &str) -> String { + format!("{}[{}]", name, state_name) +} + +/// Expression for a COUNT(DISTINCT) aggregation. +#[derive(Debug)] +pub struct DistinctCount { + /// Column name + name: String, + /// The DataType for the final count + data_type: DataType, + /// The DataType for each input argument + input_data_types: Vec<DataType>, + /// The input arguments + exprs: Vec<Arc<dyn PhysicalExpr>>, +} + +impl DistinctCount { + /// Create a new COUNT(DISTINCT) aggregate function. + pub fn new( + input_data_types: Vec<DataType>, + exprs: Vec<Arc<dyn PhysicalExpr>>, + name: String, + data_type: DataType, + ) -> Self { + Self { + input_data_types, + exprs, + name, + data_type, + } + } +} + +impl AggregateExpr for DistinctCount { + fn field(&self) -> Result<Field> { + Ok(Field::new(&self.name, self.data_type.clone(), false)) + } + + fn state_fields(&self) -> Result<Vec<Field>> { + Ok(self + .input_data_types + .iter() + .map(|data_type| { + Field::new( + &format_state_name(&self.name, "count distinct"), + DataType::List(Box::new(data_type.clone())), + false, + ) + }) + .collect::<Vec<_>>()) + } + + fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>> { + self.exprs.clone() + } + + fn create_accumulator(&self) -> Result<Rc<RefCell<dyn Accumulator>>> { + Ok(Rc::new(RefCell::new(DistinctCountAccumulator { + values: FnvHashSet::default(), + data_types: self.input_data_types.clone(), + count_data_type: self.data_type.clone(), + }))) + } +} + +#[derive(Debug)] +struct DistinctCountAccumulator { + values: FnvHashSet<DistinctScalarValues>, + data_types: Vec<DataType>, + count_data_type: DataType, +} + +impl Accumulator for DistinctCountAccumulator { + fn update_batch(&mut self, arrays: &Vec<ArrayRef>) -> Result<()> { Review comment: I made the switch (see d61ec97). For now I think the DRY approach makes sense, and as a follow-up I can explore how the different options perform. I can use [benches/aggregate_query_sql.rs](https://github.com/apache/arrow/blob/master/rust/datafusion/benches/aggregate_query_sql.rs) as a starting point for the comparisons, if that makes sense? ########## File path: rust/datafusion/src/test/mod.rs ########## @@ -135,6 +135,13 @@ pub fn format_batch(batch: &RecordBatch) -> Vec<String> { } let array = batch.column(column_index); match array.data_type() { + DataType::Utf8 => s.push_str( + array + .as_any() + .downcast_ref::<array::StringArray>() + .unwrap() + .value(row_index), + ), Review comment: No problem! This makes perfect sense, and I added the test (2d0999a). However, I also had to make the `count(distinct)` field nullable (4cdb951), otherwise I ran into an assertion error [here](https://github.com/apache/arrow/blob/2d0999ac7f1d01a4fe392add53720ceeb6b0b1f3/rust/datafusion/tests/sql.rs#L652) due to a mismatch of the field's nullability between the logical plan and physical plan. The logical plan nullability is set [here](https://github.com/apache/arrow/blob/2d0999ac7f1d01a4fe392add53720ceeb6b0b1f3/rust/datafusion/src/logical_plan/mod.rs#L298), and is always nullable. All of the regular aggregate expressions mark their field as nullable, for example, [here](https://github.com/apache/arrow/blob/2d0999ac7f1d01a4fe392add53720ceeb6b0b1f3/rust/datafusion/src/physical_plan/expressions.rs#L846) for the regular `Count`. I might be mistaken, but I think regular and distinct counts should be non-nullable? In any case, I went with making `count(distinct)` nullable for consistency with `count()`. Perhaps there's a follow-up here? ########## File path: rust/datafusion/src/physical_plan/aggregates.rs ########## @@ -124,14 +126,30 @@ pub fn create_aggregate_expr( let return_type = return_type(&fun, &arg_types)?; - Ok(match fun { - AggregateFunction::Count => { + Ok(match (fun, distinct) { + (AggregateFunction::Count, false) => { Arc::new(expressions::Count::new(arg, name, return_type)) } - AggregateFunction::Sum => Arc::new(expressions::Sum::new(arg, name, return_type)), - AggregateFunction::Min => Arc::new(expressions::Min::new(arg, name, return_type)), - AggregateFunction::Max => Arc::new(expressions::Max::new(arg, name, return_type)), - AggregateFunction::Avg => Arc::new(expressions::Avg::new(arg, name, return_type)), + (AggregateFunction::Count, true) => { + Arc::new(distinct_expressions::DistinctCount::new( + arg_types, + args.clone(), + name, + return_type, + )) + } + (AggregateFunction::Sum, _) => { Review comment: I made the change, see 7f073f7. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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