datafusion_functions/core/
union_extract.rs

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
18use arrow::array::Array;
19use arrow::datatypes::{DataType, FieldRef, UnionFields};
20use datafusion_common::cast::as_union_array;
21use datafusion_common::utils::take_function_args;
22use datafusion_common::{
23    exec_datafusion_err, exec_err, internal_err, Result, ScalarValue,
24};
25use datafusion_doc::Documentation;
26use datafusion_expr::{ColumnarValue, ReturnInfo, ReturnTypeArgs, ScalarFunctionArgs};
27use datafusion_expr::{ScalarUDFImpl, Signature, Volatility};
28use datafusion_macros::user_doc;
29
30#[user_doc(
31    doc_section(label = "Union Functions"),
32    description = "Returns the value of the given field in the union when selected, or NULL otherwise.",
33    syntax_example = "union_extract(union, field_name)",
34    sql_example = r#"```sql
35❯ select union_column, union_extract(union_column, 'a'), union_extract(union_column, 'b') from table_with_union;
36+--------------+----------------------------------+----------------------------------+
37| union_column | union_extract(union_column, 'a') | union_extract(union_column, 'b') |
38+--------------+----------------------------------+----------------------------------+
39| {a=1}        | 1                                |                                  |
40| {b=3.0}      |                                  | 3.0                              |
41| {a=4}        | 4                                |                                  |
42| {b=}         |                                  |                                  |
43| {a=}         |                                  |                                  |
44+--------------+----------------------------------+----------------------------------+
45```"#,
46    standard_argument(name = "union", prefix = "Union"),
47    argument(
48        name = "field_name",
49        description = "String expression to operate on. Must be a constant."
50    )
51)]
52#[derive(Debug)]
53pub struct UnionExtractFun {
54    signature: Signature,
55}
56
57impl Default for UnionExtractFun {
58    fn default() -> Self {
59        Self::new()
60    }
61}
62
63impl UnionExtractFun {
64    pub fn new() -> Self {
65        Self {
66            signature: Signature::any(2, Volatility::Immutable),
67        }
68    }
69}
70
71impl ScalarUDFImpl for UnionExtractFun {
72    fn as_any(&self) -> &dyn std::any::Any {
73        self
74    }
75
76    fn name(&self) -> &str {
77        "union_extract"
78    }
79
80    fn signature(&self) -> &Signature {
81        &self.signature
82    }
83
84    fn return_type(&self, _: &[DataType]) -> Result<DataType> {
85        // should be using return_type_from_exprs and not calling the default implementation
86        internal_err!("union_extract should return type from exprs")
87    }
88
89    fn return_type_from_args(&self, args: ReturnTypeArgs) -> Result<ReturnInfo> {
90        if args.arg_types.len() != 2 {
91            return exec_err!(
92                "union_extract expects 2 arguments, got {} instead",
93                args.arg_types.len()
94            );
95        }
96
97        let DataType::Union(fields, _) = &args.arg_types[0] else {
98            return exec_err!(
99                "union_extract first argument must be a union, got {} instead",
100                args.arg_types[0]
101            );
102        };
103
104        let Some(ScalarValue::Utf8(Some(field_name))) = &args.scalar_arguments[1] else {
105            return exec_err!(
106                "union_extract second argument must be a non-null string literal, got {} instead",
107                args.arg_types[1]
108            );
109        };
110
111        let field = find_field(fields, field_name)?.1;
112
113        Ok(ReturnInfo::new_nullable(field.data_type().clone()))
114    }
115
116    fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> {
117        let [array, target_name] = take_function_args("union_extract", args.args)?;
118
119        let target_name = match target_name {
120            ColumnarValue::Scalar(ScalarValue::Utf8(Some(target_name))) => Ok(target_name),
121            ColumnarValue::Scalar(ScalarValue::Utf8(None)) => exec_err!("union_extract second argument must be a non-null string literal, got a null instead"),
122            _ => exec_err!("union_extract second argument must be a non-null string literal, got {} instead", target_name.data_type()),
123        }?;
124
125        match array {
126            ColumnarValue::Array(array) => {
127                let union_array = as_union_array(&array).map_err(|_| {
128                    exec_datafusion_err!(
129                        "union_extract first argument must be a union, got {} instead",
130                        array.data_type()
131                    )
132                })?;
133
134                Ok(ColumnarValue::Array(
135                    arrow::compute::kernels::union_extract::union_extract(
136                        union_array,
137                        &target_name,
138                    )?,
139                ))
140            }
141            ColumnarValue::Scalar(ScalarValue::Union(value, fields, _)) => {
142                let (target_type_id, target) = find_field(&fields, &target_name)?;
143
144                let result = match value {
145                    Some((type_id, value)) if target_type_id == type_id => *value,
146                    _ => ScalarValue::try_new_null(target.data_type())?,
147                };
148
149                Ok(ColumnarValue::Scalar(result))
150            }
151            other => exec_err!(
152                "union_extract first argument must be a union, got {} instead",
153                other.data_type()
154            ),
155        }
156    }
157
158    fn documentation(&self) -> Option<&Documentation> {
159        self.doc()
160    }
161}
162
163fn find_field<'a>(fields: &'a UnionFields, name: &str) -> Result<(i8, &'a FieldRef)> {
164    fields
165        .iter()
166        .find(|field| field.1.name() == name)
167        .ok_or_else(|| exec_datafusion_err!("field {name} not found on union"))
168}
169
170#[cfg(test)]
171mod tests {
172
173    use arrow::datatypes::{DataType, Field, UnionFields, UnionMode};
174    use datafusion_common::{Result, ScalarValue};
175    use datafusion_expr::{ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl};
176
177    use super::UnionExtractFun;
178
179    // when it becomes possible to construct union scalars in SQL, this should go to sqllogictests
180    #[test]
181    fn test_scalar_value() -> Result<()> {
182        let fun = UnionExtractFun::new();
183
184        let fields = UnionFields::new(
185            vec![1, 3],
186            vec![
187                Field::new("str", DataType::Utf8, false),
188                Field::new("int", DataType::Int32, false),
189            ],
190        );
191
192        let result = fun.invoke_with_args(ScalarFunctionArgs {
193            args: vec![
194                ColumnarValue::Scalar(ScalarValue::Union(
195                    None,
196                    fields.clone(),
197                    UnionMode::Dense,
198                )),
199                ColumnarValue::Scalar(ScalarValue::new_utf8("str")),
200            ],
201            number_rows: 1,
202            return_type: &DataType::Utf8,
203        })?;
204
205        assert_scalar(result, ScalarValue::Utf8(None));
206
207        let result = fun.invoke_with_args(ScalarFunctionArgs {
208            args: vec![
209                ColumnarValue::Scalar(ScalarValue::Union(
210                    Some((3, Box::new(ScalarValue::Int32(Some(42))))),
211                    fields.clone(),
212                    UnionMode::Dense,
213                )),
214                ColumnarValue::Scalar(ScalarValue::new_utf8("str")),
215            ],
216            number_rows: 1,
217            return_type: &DataType::Utf8,
218        })?;
219
220        assert_scalar(result, ScalarValue::Utf8(None));
221
222        let result = fun.invoke_with_args(ScalarFunctionArgs {
223            args: vec![
224                ColumnarValue::Scalar(ScalarValue::Union(
225                    Some((1, Box::new(ScalarValue::new_utf8("42")))),
226                    fields.clone(),
227                    UnionMode::Dense,
228                )),
229                ColumnarValue::Scalar(ScalarValue::new_utf8("str")),
230            ],
231            number_rows: 1,
232            return_type: &DataType::Utf8,
233        })?;
234
235        assert_scalar(result, ScalarValue::new_utf8("42"));
236
237        Ok(())
238    }
239
240    fn assert_scalar(value: ColumnarValue, expected: ScalarValue) {
241        match value {
242            ColumnarValue::Array(array) => panic!("expected scalar got {array:?}"),
243            ColumnarValue::Scalar(scalar) => assert_eq!(scalar, expected),
244        }
245    }
246}
datafusion_functions/core/union_extract.rs

datafusion_functions/core/
union_extract.rs
