zclllyybb commented on issue #64720:
URL: https://github.com/apache/doris/issues/64720#issuecomment-4775360566
Breakwater-GitHub-Analysis-Slot: slot_525edce557da
This content is generated by AI for reference only.
Initial analysis:
This looks like a code regression, not a user-side issue. I checked the
reported 4.1.2 release line against local tag `4.1.2-rc01`, and the current
code path explains the empty result.
Evidence:
- The published 4.x `EXPLODE_SPLIT` docs say that when `<str>` is an empty
string or cannot be split, `explode_split` should return one row; the docs also
show `explode_split("", ",")` returning one row with an empty string.
- In 4.1.2, `ExplodeSplit.rewriteWhenAnalyze()` rewrites `explode_split(str,
delimiter)` to `explode(split_by_string(str, delimiter))`. `ExplodeSplitOuter`
similarly rewrites to `explode_outer(split_by_string(...))`.
- Both FE constant folding and BE scalar execution for `split_by_string`
explicitly return an empty array for an empty source string. The generated
regression output currently expects `split_by_string('', ',')` to be `[]`.
- The table-function operator skips a child row when a non-outer table
function has an empty result. Therefore `explode(split_by_string("", ","))`
produces no rows, which matches the reported behavior.
- This differs from the older 3.x implementation. In `3.0.8-rc02`,
`explode_split` still had a dedicated BE `VExplodeSplitTableFunction`; its
split loop produced one empty `StringRef` for an empty input string, so normal
`explode_split("", ",")` emitted one empty-string row. That implementation was
removed by public PR #54886 / commit `39ab12d3e80` (`Rewrite explode_split to
explode + split_by_string`).
- I also checked freshly fetched `upstream/master`; the same `explode_split
-> explode(split_by_string(...))` rewrite and the same `split_by_string`
empty-source branch are still present, so this does not appear fixed on master
from the inspected code path.
Suggested next steps:
1. Add regression coverage for `select * from example lateral view
explode_split("", ",") t as c;`, expecting one row with an empty string.
2. Decide the fix boundary:
- If the published 4.x `SPLIT_BY_STRING` docs are authoritative too, fix
`split_by_string("", non_null_delimiter)` to return `[""]`, then
`explode_split` will naturally return one row.
- If changing scalar `split_by_string` is considered incompatible with
existing behavior/tests, add an `explode_split`-specific compatibility path so
`explode_split` preserves the documented 3.x/table-function behavior without
globally changing `split_by_string`.
3. Recheck `explode_split_outer("", ",")`, `explode_split(NULL, ",")`,
delimiter `NULL`, and empty delimiter cases with the same regression suite so
the fix does not blur normal `explode` and `explode_outer` semantics.
No additional logs or runtime profile are needed for the first code-level
fix. The main missing input is the maintainer decision on whether the
compatibility fix should be applied globally to `split_by_string` or scoped
only to `explode_split`.
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