neilconway opened a new issue, #24152:
URL: https://github.com/apache/datafusion/issues/24152
### Describe the bug
How `regexp_count` handles NULL is inconsistent with PostgreSQL; it is also
not self-consistent:
| Query | DataFusion | PostgreSQL |
|---|---|---|
| `regexp_count(NULL, 'a')` | 0 | NULL |
| `regexp_count('a', NULL)` | 0 | NULL |
| `regexp_count('abc', 'b', NULL)` | error: `regexp_count() requires start
to be 1 based` | NULL |
| `regexp_count(v, 'b', s)` with rows `('abc', 1)`, `('abcb', NULL)` | `1`,
`2` — NULL start treated as 1 | `1`, `NULL` |
| `regexp_count('abc', 'b', 1, NULL)` | 1 — NULL flags treated as absent |
NULL |
### To Reproduce
_No response_
### Expected behavior
Match what Postgres does.
### Additional context
_No response_
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