dd-david-levin opened a new pull request, #21104:
URL: https://github.com/apache/datafusion/pull/21104
## Problem
`string_to_array('', ',')` was returning `['']` (an array containing one
empty string) instead of `[]` (an empty array), which is incorrect according to
PostgreSQL behavior.
**Root cause:** Rust's `str::split()` on an empty string always yields one
empty-string element. So `"".split(",")` produces `[""]`, which was being
appended to the list builder as-is.
**PostgreSQL expected behavior** (see
[db-fiddle](https://www.db-fiddle.com/f/oCF8EPaZFkDNKSg28rVVWy/0)):
```sql
SELECT string_to_array('', ',');
-- {} (empty array)
```
## Fix
Added an `is_empty()` guard in `string_to_array_impl` in
`datafusion/functions-nested/src/string.rs`. When the input string is empty and
the delimiter is a non-empty string, we now append an empty list instead of
splitting. The fix applies to both the plain variant and the `null_value`
variant of the function.
## Test
Added a sqllogictest case in `datafusion/sqllogictest/test_files/array.slt`:
```sql
SELECT string_to_array('', ',')
----
[]
```
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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