datafusion_functions/core/
overlay.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 std::sync::Arc;
19
20use arrow::array::{ArrayRef, GenericStringArray, OffsetSizeTrait};
21use arrow::datatypes::DataType;
22
23use crate::utils::{make_scalar_function, utf8_to_str_type};
24use datafusion_common::cast::{
25    as_generic_string_array, as_int64_array, as_string_view_array,
26};
27use datafusion_common::{Result, exec_err};
28use datafusion_expr::{ColumnarValue, Documentation, TypeSignature, Volatility};
29use datafusion_expr::{ScalarFunctionArgs, ScalarUDFImpl, Signature};
30use datafusion_macros::user_doc;
31
32#[user_doc(
33    doc_section(label = "String Functions"),
34    description = "Returns the string which is replaced by another string from the specified position and specified count length.",
35    syntax_example = "overlay(str PLACING substr FROM pos [FOR count])",
36    sql_example = r#"```sql
37> select overlay('Txxxxas' placing 'hom' from 2 for 4);
38+--------------------------------------------------------+
39| overlay(Utf8("Txxxxas"),Utf8("hom"),Int64(2),Int64(4)) |
40+--------------------------------------------------------+
41| Thomas                                                 |
42+--------------------------------------------------------+
43```"#,
44    standard_argument(name = "str", prefix = "String"),
45    argument(name = "substr", description = "Substring to replace in str."),
46    argument(
47        name = "pos",
48        description = "The start position to start the replace in str."
49    ),
50    argument(
51        name = "count",
52        description = "The count of characters to be replaced from start position of str. If not specified, will use substr length instead."
53    )
54)]
55#[derive(Debug, PartialEq, Eq, Hash)]
56pub struct OverlayFunc {
57    signature: Signature,
58}
59
60impl Default for OverlayFunc {
61    fn default() -> Self {
62        Self::new()
63    }
64}
65
66impl OverlayFunc {
67    pub fn new() -> Self {
68        use DataType::*;
69        Self {
70            signature: Signature::one_of(
71                vec![
72                    TypeSignature::Exact(vec![Utf8View, Utf8View, Int64, Int64]),
73                    TypeSignature::Exact(vec![Utf8, Utf8, Int64, Int64]),
74                    TypeSignature::Exact(vec![LargeUtf8, LargeUtf8, Int64, Int64]),
75                    TypeSignature::Exact(vec![Utf8View, Utf8View, Int64]),
76                    TypeSignature::Exact(vec![Utf8, Utf8, Int64]),
77                    TypeSignature::Exact(vec![LargeUtf8, LargeUtf8, Int64]),
78                ],
79                Volatility::Immutable,
80            ),
81        }
82    }
83}
84
85impl ScalarUDFImpl for OverlayFunc {
86    fn name(&self) -> &str {
87        "overlay"
88    }
89
90    fn signature(&self) -> &Signature {
91        &self.signature
92    }
93
94    fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
95        utf8_to_str_type(&arg_types[0], "overlay")
96    }
97
98    fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> {
99        match args.args[0].data_type() {
100            DataType::Utf8View | DataType::Utf8 => {
101                make_scalar_function(overlay::<i32>, vec![])(&args.args)
102            }
103            DataType::LargeUtf8 => {
104                make_scalar_function(overlay::<i64>, vec![])(&args.args)
105            }
106            other => exec_err!("Unsupported data type {other:?} for function overlay"),
107        }
108    }
109
110    fn documentation(&self) -> Option<&Documentation> {
111        self.doc()
112    }
113}
114
115/// Converts a 0-based character index into a byte index suitable for UTF-8
116/// slicing.
117fn byte_index_for_char(string: &str, char_idx: usize, is_ascii: bool) -> usize {
118    if is_ascii {
119        char_idx.min(string.len())
120    } else {
121        string
122            .char_indices()
123            .nth(char_idx)
124            .map_or(string.len(), |(byte_idx, _)| byte_idx)
125    }
126}
127
128/// Builds the OVERLAY result for a single (non-null) row.
129///
130/// `start_pos` is a 1-based character position; `replace_len` is the number
131/// of characters of `string` to replace with `characters`.
132fn overlay_one(
133    string: &str,
134    characters: &str,
135    start_pos: i64,
136    replace_len: i64,
137) -> Result<String> {
138    if start_pos < 1 {
139        return exec_err!("negative substring length not allowed");
140    }
141
142    let is_ascii = string.is_ascii();
143    let string_char_len = if is_ascii {
144        string.len() as i64
145    } else {
146        string.chars().count() as i64
147    };
148
149    // Convert SQL's 1-based character position into 0-based character indexes.
150    // `start_char_idx` is the first replaced character; `end_char_idx` is the
151    // first character after the replaced span.
152    //
153    // No upper-bound check on `start_char_idx`: when it exceeds `string_char_len`
154    // we want the whole string as the prefix (PostgreSQL-compatible "insert past
155    // end" semantics).
156    let start_char_idx = start_pos - 1;
157    let end_char_idx = start_char_idx.saturating_add(replace_len);
158
159    let prefix_char_idx = usize::try_from(start_char_idx).unwrap_or(usize::MAX);
160    let prefix_end_byte = byte_index_for_char(string, prefix_char_idx, is_ascii);
161
162    let mut res = String::with_capacity(string.len() + characters.len());
163    res.push_str(&string[..prefix_end_byte]);
164    res.push_str(characters);
165
166    if end_char_idx < string_char_len {
167        let suffix_char_idx = usize::try_from(end_char_idx.max(0)).unwrap_or(usize::MAX);
168        let suffix_start_byte = byte_index_for_char(string, suffix_char_idx, is_ascii);
169        res.push_str(&string[suffix_start_byte..]);
170    }
171    Ok(res)
172}
173
174macro_rules! process_overlay {
175    // Three argument case
176    ($string_array:expr, $characters_array:expr, $pos_array:expr) => {{
177        $string_array
178            .iter()
179            .zip($characters_array.iter())
180            .zip($pos_array.iter())
181            .map(|((string, characters), start_pos)| {
182                match (string, characters, start_pos) {
183                    (Some(string), Some(characters), Some(start_pos)) => {
184                        let replace_len = characters.chars().count() as i64;
185                        overlay_one(string, characters, start_pos, replace_len).map(Some)
186                    }
187                    _ => Ok(None),
188                }
189            })
190            .collect::<Result<GenericStringArray<T>>>()
191    }};
192
193    // Four argument case
194    ($string_array:expr, $characters_array:expr, $pos_array:expr, $len_array:expr) => {{
195        $string_array
196            .iter()
197            .zip($characters_array.iter())
198            .zip($pos_array.iter())
199            .zip($len_array.iter())
200            .map(|(((string, characters), start_pos), replace_len)| {
201                match (string, characters, start_pos, replace_len) {
202                    (
203                        Some(string),
204                        Some(characters),
205                        Some(start_pos),
206                        Some(replace_len),
207                    ) => {
208                        overlay_one(string, characters, start_pos, replace_len).map(Some)
209                    }
210                    _ => Ok(None),
211                }
212            })
213            .collect::<Result<GenericStringArray<T>>>()
214    }};
215}
216
217/// `OVERLAY(string PLACING substring FROM start [FOR count])`
218///
219/// Replaces a region of `string` with `substring`, starting at the 1-based
220/// character position `start`. If `count` is supplied, that many characters
221/// of `string` are replaced; otherwise `count` defaults to the character
222/// length of `substring`.
223///
224/// ```text
225/// overlay('Txxxxas' placing 'hom' from 2 for 4) → 'Thomas'
226/// overlay('Txxxxas' placing 'hom' from 2)       → 'Thomxas'
227/// ```
228fn overlay<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
229    if !matches!(args.len(), 3 | 4) {
230        return exec_err!(
231            "overlay was called with {} arguments. It requires 3 or 4.",
232            args.len()
233        );
234    }
235    if args[0].data_type() == &DataType::Utf8View {
236        string_view_overlay::<T>(args)
237    } else {
238        string_overlay::<T>(args)
239    }
240}
241
242fn string_overlay<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
243    let string_array = as_generic_string_array::<T>(&args[0])?;
244    let characters_array = as_generic_string_array::<T>(&args[1])?;
245    let pos_array = as_int64_array(&args[2])?;
246
247    let result = if args.len() == 4 {
248        let len_array = as_int64_array(&args[3])?;
249        process_overlay!(string_array, characters_array, pos_array, len_array)?
250    } else {
251        process_overlay!(string_array, characters_array, pos_array)?
252    };
253    Ok(Arc::new(result) as ArrayRef)
254}
255
256fn string_view_overlay<T: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
257    let string_array = as_string_view_array(&args[0])?;
258    let characters_array = as_string_view_array(&args[1])?;
259    let pos_array = as_int64_array(&args[2])?;
260
261    let result = if args.len() == 4 {
262        let len_array = as_int64_array(&args[3])?;
263        process_overlay!(string_array, characters_array, pos_array, len_array)?
264    } else {
265        process_overlay!(string_array, characters_array, pos_array)?
266    };
267    Ok(Arc::new(result) as ArrayRef)
268}
269
270#[cfg(test)]
271mod tests {
272    use arrow::array::{Int64Array, StringArray};
273
274    use super::*;
275
276    #[test]
277    fn to_overlay() -> Result<()> {
278        let string =
279            Arc::new(StringArray::from(vec!["123", "abcdefg", "xyz", "Txxxxas"]));
280        let replace_string =
281            Arc::new(StringArray::from(vec!["abc", "qwertyasdfg", "ijk", "hom"]));
282        let start = Arc::new(Int64Array::from(vec![4, 1, 1, 2])); // start
283        let end = Arc::new(Int64Array::from(vec![5, 7, 2, 4])); // replace len
284
285        let res = overlay::<i32>(&[string, replace_string, start, end]).unwrap();
286        let result = as_generic_string_array::<i32>(&res).unwrap();
287        // First row: start=4 is past the end of "123" (len 3). PostgreSQL
288        // takes the whole string as prefix and appends the replacement.
289        let expected = StringArray::from(vec!["123abc", "qwertyasdfg", "ijkz", "Thomas"]);
290        assert_eq!(&expected, result);
291
292        Ok(())
293    }
294}
datafusion_functions/core/overlay.rs

datafusion_functions/core/
overlay.rs
