linrrzqqq opened a new pull request, #68146:
URL: https://github.com/apache/doris/pull/68146
### What problem does this PR solve?
Issue Number: close #xxx
Related PR: #xxx
Problem Summary:
An empty regexp produces a zero-width match, so the expected result is 1.
The constant pattern was recognized as a substring pattern and routed to the
long-buffer substring optimization. However, this path treated an empty needle
as not found.
```sql
DROP TABLE IF EXISTS tmp_b8_c01;
CREATE TABLE tmp_b8_c01 (
id INT,
s STRING,
p STRING
)
DUPLICATE KEY(id)
DISTRIBUTED BY HASH(id) BUCKETS 1
PROPERTIES("replication_num" = "1");
INSERT INTO tmp_b8_c01 VALUES (1, 'abc', '');
SELECT
regexp('abc', '') AS const_empty,
regexp(s, p) AS column_empty
FROM tmp_b8_c01
WHERE id = 1;
-- before:
+-------------+--------------+
| const_empty | column_empty |
+-------------+--------------+
| 0 | 1 |
+-------------+--------------+
-- now:
+-------------+--------------+
| const_empty | column_empty |
+-------------+--------------+
| 1 | 1 |
+-------------+--------------+
```
### What is changed?
- Handle an empty constant substring pattern as matching every non-null
input.
- Move the long-buffer substring implementation into `constant_substring_fn`.
- Remove the separate execute_substring implementation and its special
dispatch logic.
- Preserve row-boundary checks to prevent matches across adjacent
ColumnString rows.
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