lonless9 opened a new issue, #27120:
URL: https://github.com/apache/datafusion/issues/27120
### Describe the bug
A regex matching a literal backslash is rewritten to a LIKE pattern with
different escaping semantics, producing both false positives and false
negatives.
Reproduced in 55.2.0 and 56.0.0-dev (1635ed947).
### To Reproduce
Create regex.csv:
```csv
id,s,p
1,a\b,a\\b
2,ab,a\\b
```
Run:
```sql
CREATE EXTERNAL TABLE regex_input (
id BIGINT, s VARCHAR, p VARCHAR
)
STORED AS CSV LOCATION 'regex.csv'
OPTIONS ('has_header' 'true');
SELECT
id,
s ~ ('a' || chr(92) || chr(92) || 'b') AS constant_pattern,
s ~ p AS dynamic_pattern
FROM regex_input
ORDER BY id;
```
Expected:
```text
id | constant_pattern | dynamic_pattern
1 | true | true
2 | false | false
```
Actual:
```text
id | constant_pattern | dynamic_pattern
1 | false | true
2 | true | false
```
The constant pattern is optimized into LIKE '%a\b%', where the backslash is
consumed as a LIKE escape. The dynamic pattern retains the correct regex
behavior.
### Expected behavior
_No response_
### Additional context
_No response_
### Willingness to contribute
None
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