`split_part` with position 0 errors on a NULL string only when the position is a literal

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Seit 12.11.2026.

  • #27352 von @sohailshk — offen

Bewertung

Schwierigkeit
3/5
Geschätzter Aufwand
1-2 Tage
Anfängerfreundlichkeit
48/100
Issue-Typ
Bug
Klarheit
Größtenteils klar
Aktivitätsstatus
Aktiv
Tech-Stack
rust, sql
Bereich
backend, databases, testing-qa

Rechercherichtung

Start with datafusion/functions/src/string/split_part.rs, especially the fast path and the array path identified in the issue, then review the expr.slt case around the reported test. Decide how the fast path should behave when every string is NULL, using the stated PostgreSQL strictness expectation and the prior review discussion as context. Update the regression test to reflect the chosen behavior and verify the literal and column position cases agree.

Vom Indexierungsmodell aus dem Issue-Text verfasst.

Beschreibung

bug

Describe the bug

split_part(s, delimiter, 0) on a row where s is NULL returns NULL when the position comes from a column, and errors with "field position must not be zero" when the position is a literal. The fast path for an array string with a scalar delimiter and position rejects position 0 before it looks at any row. The array path skips rows where any argument is NULL, so it errors only on a row whose three arguments are all non-NULL. The two paths disagree whenever no row has a non-NULL string, such as a batch whose strings are all NULL.

To Reproduce

-- Literal delimiter and position: the fast path
SELECT split_part(s, '.', 0) AS r FROM (VALUES (NULL::text)) AS t(s);
-- Execution error: field position must not be zero

-- The same row with the position from a column: the array path
SELECT split_part(s, '.', p) AS r FROM (VALUES (NULL::text, 0)) AS t(s, p);
-- NULL

-- Only literals
SELECT split_part(NULL::text, '.', 0) AS r;
-- NULL

Expected behavior

All three return NULL. PostgreSQL's split_part is strict: its pg_proc entry leaves proisstrict at its default of true, so a NULL argument returns NULL without calling the function.

expr.slt expects the first query's error ("Position 0 with column input errors even for empty/null inputs"), while the review of #21238 asked for the fast path to match the array path (discussion_r3030106101). Which behavior is intended? If it is NULL, the fast path could return all NULLs when the string array has no valid row before checking the position, and the expr.slt case would expect NULL.

Additional context

Property-based tests found this on main at 14b3edd9a3: calling split_part with an array string and scalar delimiter and position gave an error, and the same call with every argument as an array gave NULL. The reproduction runs on main at 14b3edd9a3. The fast path came with #21238.

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Rust
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Gemergte PRs (30 T.)
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