alamb commented on code in PR #7981:
URL: https://github.com/apache/arrow-datafusion/pull/7981#discussion_r1380703847
##########
datafusion/expr/src/logical_plan/plan.rs:
##########
@@ -2132,9 +2181,100 @@ pub struct Limit {
/// Removes duplicate rows from the input
#[derive(Clone, PartialEq, Eq, Hash)]
-pub struct Distinct {
+pub enum Distinct {
+ /// Plain `DISTINCT` referencing all selection expressions
+ All(Arc<LogicalPlan>),
+ /// The `Postgres` addition, allowing separate control over DISTINCT'd and
selected columns
+ On(DistinctOn),
+}
+
+/// Removes duplicate rows from the input
+#[derive(Clone, PartialEq, Eq, Hash)]
+pub struct DistinctOn {
+ /// The `DISTINCT ON` clause expression list
+ pub on_expr: Vec<Expr>,
+ /// The selected projection expression list
+ pub select_expr: Vec<Expr>,
+ /// The `ORDER BY` clause, whose initial expressions must match those of
the `ON` clause
Review Comment:
Since the same list of exprs is included in both the `select_list` and
`sort_exprs` I wonder if it would be less error prone to have references rather
than keep three parallel lists:
```
/// The selected projection expression list
pub select_expr: Vec<Expr>,
/// The sort expressions
pub sort_expr: Vec<Expr>,
/// the number of prefix columns from `sort_expr` that form the `ON`
clause used for deduplicating
##########
datafusion/optimizer/src/replace_distinct_aggregate.rs:
##########
@@ -32,6 +36,22 @@ use datafusion_expr::{Aggregate, Distinct, LogicalPlan};
/// ```text
/// SELECT a, b FROM tab GROUP BY a, b
/// ```
+///
+/// On the other hand, for a `DISTINCT ON` query the replacement is
+/// a bit more involved and effectively converts
+/// ```text
+/// SELECT DISTINCT ON (a) b FROM tab ORDER BY a DESC, c
+/// ```
+///
+/// into
+/// ```text
+/// SELECT b FROM (
+/// SELECT a, FIRST_VALUE(b ORDER BY a DESC, c) AS b
Review Comment:
```suggestion
/// SELECT a, FIRST_VALUE(PARTITION BY b ORDER BY a DESC, c) AS b
```
##########
datafusion/optimizer/src/replace_distinct_aggregate.rs:
##########
@@ -32,6 +36,22 @@ use datafusion_expr::{Aggregate, Distinct, LogicalPlan};
/// ```text
/// SELECT a, b FROM tab GROUP BY a, b
/// ```
+///
+/// On the other hand, for a `DISTINCT ON` query the replacement is
Review Comment:
Thank you -- this is very helpful to understand what is going on
##########
datafusion/sqllogictest/test_files/distinct_on.slt:
##########
@@ -0,0 +1,129 @@
+# 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.
+
+statement ok
+CREATE EXTERNAL TABLE aggregate_test_100 (
+ c1 VARCHAR NOT NULL,
+ c2 TINYINT NOT NULL,
+ c3 SMALLINT NOT NULL,
+ c4 SMALLINT,
+ c5 INT,
+ c6 BIGINT NOT NULL,
+ c7 SMALLINT NOT NULL,
+ c8 INT NOT NULL,
+ c9 BIGINT UNSIGNED NOT NULL,
+ c10 VARCHAR NOT NULL,
+ c11 FLOAT NOT NULL,
+ c12 DOUBLE NOT NULL,
+ c13 VARCHAR NOT NULL
+)
+STORED AS CSV
+WITH HEADER ROW
+LOCATION '../../testing/data/csv/aggregate_test_100.csv'
+
+# Basic example: distinct on the first column project the second one, and
+# order by the third
+# TODO: Note that the value for 'a' is actually degenerate, and while Postgres
+# returns the actual first match (4), DataFusion returns the last one,
presumably
+# because `first_value` aggregation function doesn't have a dedicated
`GroupsAccumulator`
Review Comment:
this doesn't make sense to me -- we should get the correct values,
regardless of the presence of a groups accumulator
##########
datafusion/optimizer/src/common_subexpr_eliminate.rs:
##########
@@ -458,16 +467,19 @@ fn build_common_expr_project_plan(
/// the "intermediate" projection plan built in
[build_common_expr_project_plan].
///
/// This is for those plans who don't keep its own output schema like `Filter`
or `Sort`.
-fn build_recover_project_plan(schema: &DFSchema, input: LogicalPlan) ->
LogicalPlan {
+fn build_recover_project_plan(
+ schema: &DFSchema,
+ input: LogicalPlan,
+) -> Result<LogicalPlan> {
let col_exprs = schema
.fields()
.iter()
.map(|field| Expr::Column(field.qualified_column()))
.collect();
- LogicalPlan::Projection(
- Projection::try_new(col_exprs, Arc::new(input))
- .expect("Cannot build projection plan from an invalid schema"),
- )
+ Ok(LogicalPlan::Projection(Projection::try_new(
Review Comment:
👍
##########
datafusion/optimizer/src/common_subexpr_eliminate.rs:
##########
@@ -458,16 +467,19 @@ fn build_common_expr_project_plan(
/// the "intermediate" projection plan built in
[build_common_expr_project_plan].
///
/// This is for those plans who don't keep its own output schema like `Filter`
or `Sort`.
-fn build_recover_project_plan(schema: &DFSchema, input: LogicalPlan) ->
LogicalPlan {
+fn build_recover_project_plan(
+ schema: &DFSchema,
+ input: LogicalPlan,
+) -> Result<LogicalPlan> {
let col_exprs = schema
.fields()
.iter()
.map(|field| Expr::Column(field.qualified_column()))
.collect();
- LogicalPlan::Projection(
- Projection::try_new(col_exprs, Arc::new(input))
- .expect("Cannot build projection plan from an invalid schema"),
- )
+ Ok(LogicalPlan::Projection(Projection::try_new(
Review Comment:
👍
##########
datafusion/optimizer/src/common_subexpr_eliminate.rs:
##########
@@ -238,8 +238,17 @@ impl CommonSubexprEliminate {
let rewritten = pop_expr(&mut rewritten)?;
if affected_id.is_empty() {
+ // Alias aggregation epxressions if they have changed
+ // TODO: This should have really been identified above and handled
in the `else` branch
+ let aggr_exprs = new_aggr_expr
+ .iter()
+ .zip(aggr_expr.iter())
+ .map(|(new_expr, old_expr)| {
+ new_expr.clone().alias_if_changed(old_expr.display_name()?)
+ })
+ .collect::<Result<Vec<Expr>>>()?;
// Since group_epxr changes, schema changes also. Use try_new
method.
- Aggregate::try_new(Arc::new(new_input), new_group_expr,
new_aggr_expr)
+ Aggregate::try_new(Arc::new(new_input), new_group_expr, aggr_exprs)
.map(LogicalPlan::Aggregate)
Review Comment:
Maybe @waynexia has some thoughts
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