/Users/andrewlamb/Software/datafusion/datafusion/physical-expr/src/window/built_in_window_function_expr.rs
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1 | | // Licensed to the Apache Software Foundation (ASF) under one |
2 | | // or more contributor license agreements. See the NOTICE file |
3 | | // distributed with this work for additional information |
4 | | // regarding copyright ownership. The ASF licenses this file |
5 | | // to you under the Apache License, Version 2.0 (the |
6 | | // "License"); you may not use this file except in compliance |
7 | | // with the License. You may obtain a copy of the License at |
8 | | // |
9 | | // http://www.apache.org/licenses/LICENSE-2.0 |
10 | | // |
11 | | // Unless required by applicable law or agreed to in writing, |
12 | | // software distributed under the License is distributed on an |
13 | | // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
14 | | // KIND, either express or implied. See the License for the |
15 | | // specific language governing permissions and limitations |
16 | | // under the License. |
17 | | |
18 | | use crate::{PhysicalExpr, PhysicalSortExpr}; |
19 | | |
20 | | use arrow::array::ArrayRef; |
21 | | use arrow::datatypes::Field; |
22 | | use arrow::record_batch::RecordBatch; |
23 | | use arrow_schema::SchemaRef; |
24 | | use datafusion_common::Result; |
25 | | use datafusion_expr::PartitionEvaluator; |
26 | | |
27 | | use std::any::Any; |
28 | | use std::sync::Arc; |
29 | | |
30 | | /// Evaluates a window function by instantiating a |
31 | | /// `[PartitionEvaluator]` for calculating the function's output in |
32 | | /// that partition. |
33 | | /// |
34 | | /// Note that unlike aggregation based window functions, some window |
35 | | /// functions such as `rank` ignore the values in the window frame, |
36 | | /// but others such as `first_value`, `last_value`, and |
37 | | /// `nth_value` need the value. |
38 | | #[allow(rustdoc::private_intra_doc_links)] |
39 | | pub trait BuiltInWindowFunctionExpr: Send + Sync + std::fmt::Debug { |
40 | | /// Returns the aggregate expression as [`Any`] so that it can be |
41 | | /// downcast to a specific implementation. |
42 | | fn as_any(&self) -> &dyn Any; |
43 | | |
44 | | /// The field of the final result of evaluating this window function. |
45 | | fn field(&self) -> Result<Field>; |
46 | | |
47 | | /// Expressions that are passed to the [`PartitionEvaluator`]. |
48 | | fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>>; |
49 | | |
50 | | /// Human readable name such as `"MIN(c2)"` or `"RANK()"`. The default |
51 | | /// implementation returns placeholder text. |
52 | 0 | fn name(&self) -> &str { |
53 | 0 | "BuiltInWindowFunctionExpr: default name" |
54 | 0 | } |
55 | | |
56 | | /// Evaluate window function's arguments against the input window |
57 | | /// batch and return an [`ArrayRef`]. |
58 | | /// |
59 | | /// Typically, the resulting vector is a single element vector. |
60 | 0 | fn evaluate_args(&self, batch: &RecordBatch) -> Result<Vec<ArrayRef>> { |
61 | 0 | self.expressions() |
62 | 0 | .iter() |
63 | 0 | .map(|e| { |
64 | 0 | e.evaluate(batch) |
65 | 0 | .and_then(|v| v.into_array(batch.num_rows())) |
66 | 0 | }) |
67 | 0 | .collect() |
68 | 0 | } |
69 | | |
70 | | /// Create a [`PartitionEvaluator`] for evaluating the function on |
71 | | /// a particular partition. |
72 | | fn create_evaluator(&self) -> Result<Box<dyn PartitionEvaluator>>; |
73 | | |
74 | | /// Construct a new [`BuiltInWindowFunctionExpr`] that produces |
75 | | /// the same result as this function on a window with reverse |
76 | | /// order. The return value of this function is used by the |
77 | | /// DataFusion optimizer to avoid re-sorting the data when |
78 | | /// possible. |
79 | | /// |
80 | | /// Returns `None` (the default) if no reverse is known (or possible). |
81 | | /// |
82 | | /// For example, the reverse of `lead(10)` is `lag(10)`. |
83 | 0 | fn reverse_expr(&self) -> Option<Arc<dyn BuiltInWindowFunctionExpr>> { |
84 | 0 | None |
85 | 0 | } |
86 | | |
87 | | /// Returns the ordering introduced by the window function, if applicable. |
88 | | /// Most window functions don't introduce an ordering, hence the default |
89 | | /// value is `None`. Note that this information is used to update ordering |
90 | | /// equivalences. |
91 | 3 | fn get_result_ordering(&self, _schema: &SchemaRef) -> Option<PhysicalSortExpr> { |
92 | 3 | None |
93 | 3 | } |
94 | | } |