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, Field, FieldRef, UnionFields};
20use datafusion_common::cast::as_union_array;
21use datafusion_common::utils::take_function_args;
22use datafusion_common::{
23    Result, ScalarValue, exec_datafusion_err, exec_err, internal_err,
24};
25use datafusion_doc::Documentation;
26use datafusion_expr::{ColumnarValue, ReturnFieldArgs, 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, PartialEq, Eq, Hash)]
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 name(&self) -> &str {
73        "union_extract"
74    }
75
76    fn signature(&self) -> &Signature {
77        &self.signature
78    }
79
80    fn return_type(&self, _: &[DataType]) -> Result<DataType> {
81        // should be using return_field_from_args and not calling the default implementation
82        internal_err!("union_extract should return type from args")
83    }
84
85    fn return_field_from_args(&self, args: ReturnFieldArgs) -> Result<FieldRef> {
86        if args.arg_fields.len() != 2 {
87            return exec_err!(
88                "union_extract expects 2 arguments, got {} instead",
89                args.arg_fields.len()
90            );
91        }
92
93        let DataType::Union(fields, _) = &args.arg_fields[0].data_type() else {
94            return exec_err!(
95                "union_extract first argument must be a union, got {} instead",
96                args.arg_fields[0].data_type()
97            );
98        };
99
100        let Some(ScalarValue::Utf8(Some(field_name))) = &args.scalar_arguments[1] else {
101            return exec_err!(
102                "union_extract second argument must be a non-null string literal, got {} instead",
103                args.arg_fields[1].data_type()
104            );
105        };
106
107        let field = find_field(fields, field_name)?.1;
108
109        Ok(Field::new(self.name(), field.data_type().clone(), true).into())
110    }
111
112    fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> {
113        let [array, target_name] = take_function_args("union_extract", args.args)?;
114
115        let target_name = match target_name {
116            ColumnarValue::Scalar(ScalarValue::Utf8(Some(target_name))) => {
117                Ok(target_name)
118            }
119            ColumnarValue::Scalar(ScalarValue::Utf8(None)) => exec_err!(
120                "union_extract second argument must be a non-null string literal, got a null instead"
121            ),
122            _ => exec_err!(
123                "union_extract second argument must be a non-null string literal, got {} instead",
124                target_name.data_type()
125            ),
126        }?;
127
128        match array {
129            ColumnarValue::Array(array) => {
130                let union_array = as_union_array(&array).map_err(|_| {
131                    exec_datafusion_err!(
132                        "union_extract first argument must be a union, got {} instead",
133                        array.data_type()
134                    )
135                })?;
136
137                Ok(ColumnarValue::Array(
138                    arrow::compute::kernels::union_extract::union_extract(
139                        union_array,
140                        &target_name,
141                    )?,
142                ))
143            }
144            ColumnarValue::Scalar(ScalarValue::Union(value, fields, _)) => {
145                let (target_type_id, target) = find_field(&fields, &target_name)?;
146
147                let result = match value {
148                    Some((type_id, value)) if target_type_id == type_id => *value,
149                    _ => ScalarValue::try_new_null(target.data_type())?,
150                };
151
152                Ok(ColumnarValue::Scalar(result))
153            }
154            other => exec_err!(
155                "union_extract first argument must be a union, got {} instead",
156                other.data_type()
157            ),
158        }
159    }
160
161    fn documentation(&self) -> Option<&Documentation> {
162        self.doc()
163    }
164}
165
166fn find_field<'a>(fields: &'a UnionFields, name: &str) -> Result<(i8, &'a FieldRef)> {
167    fields
168        .iter()
169        .find(|field| field.1.name() == name)
170        .ok_or_else(|| exec_datafusion_err!("field {name} not found on union"))
171}
172
173#[cfg(test)]
174mod tests {
175    use arrow::datatypes::{DataType, Field, UnionFields, UnionMode};
176    use datafusion_common::config::ConfigOptions;
177    use datafusion_common::{Result, ScalarValue};
178    use datafusion_expr::{ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl};
179    use std::sync::Arc;
180
181    use super::UnionExtractFun;
182
183    // when it becomes possible to construct union scalars in SQL, this should go to sqllogictests
184    #[test]
185    fn test_scalar_value() -> Result<()> {
186        let fun = UnionExtractFun::new();
187
188        let fields = UnionFields::try_new(
189            vec![1, 3],
190            vec![
191                Field::new("str", DataType::Utf8, false),
192                Field::new("int", DataType::Int32, false),
193            ],
194        )
195        .unwrap();
196
197        let args = vec![
198            ColumnarValue::Scalar(ScalarValue::Union(
199                None,
200                fields.clone(),
201                UnionMode::Dense,
202            )),
203            ColumnarValue::Scalar(ScalarValue::new_utf8("str")),
204        ];
205        let arg_fields = args
206            .iter()
207            .map(|arg| Field::new("a", arg.data_type().clone(), true).into())
208            .collect::<Vec<_>>();
209
210        let result = fun.invoke_with_args(ScalarFunctionArgs {
211            args,
212            arg_fields,
213            number_rows: 1,
214            return_field: Field::new("f", DataType::Utf8, true).into(),
215            config_options: Arc::new(ConfigOptions::default()),
216        })?;
217
218        assert_scalar(result, ScalarValue::Utf8(None));
219
220        let args = vec![
221            ColumnarValue::Scalar(ScalarValue::Union(
222                Some((3, Box::new(ScalarValue::Int32(Some(42))))),
223                fields.clone(),
224                UnionMode::Dense,
225            )),
226            ColumnarValue::Scalar(ScalarValue::new_utf8("str")),
227        ];
228        let arg_fields = args
229            .iter()
230            .map(|arg| Field::new("a", arg.data_type().clone(), true).into())
231            .collect::<Vec<_>>();
232
233        let result = fun.invoke_with_args(ScalarFunctionArgs {
234            args,
235            arg_fields,
236            number_rows: 1,
237            return_field: Field::new("f", DataType::Utf8, true).into(),
238            config_options: Arc::new(ConfigOptions::default()),
239        })?;
240
241        assert_scalar(result, ScalarValue::Utf8(None));
242
243        let args = vec![
244            ColumnarValue::Scalar(ScalarValue::Union(
245                Some((1, Box::new(ScalarValue::new_utf8("42")))),
246                fields.clone(),
247                UnionMode::Dense,
248            )),
249            ColumnarValue::Scalar(ScalarValue::new_utf8("str")),
250        ];
251        let arg_fields = args
252            .iter()
253            .map(|arg| Field::new("a", arg.data_type().clone(), true).into())
254            .collect::<Vec<_>>();
255        let result = fun.invoke_with_args(ScalarFunctionArgs {
256            args,
257            arg_fields,
258            number_rows: 1,
259            return_field: Field::new("f", DataType::Utf8, true).into(),
260            config_options: Arc::new(ConfigOptions::default()),
261        })?;
262
263        assert_scalar(result, ScalarValue::new_utf8("42"));
264
265        Ok(())
266    }
267
268    fn assert_scalar(value: ColumnarValue, expected: ScalarValue) {
269        match value {
270            ColumnarValue::Array(array) => panic!("expected scalar got {array:?}"),
271            ColumnarValue::Scalar(scalar) => assert_eq!(scalar, expected),
272        }
273    }
274}
datafusion_functions/core/union_extract.rs

datafusion_functions/core/
union_extract.rs
