Baymine opened a new pull request, #66181:
URL: https://github.com/apache/doris/pull/66181
### What problem does this PR solve?
Issue Number: close #66179
Related PR: N/A
Problem Summary:
`element_at(split_by_string(s, d), n)` builds the whole split array (a
PODArray allocation and a memcpy per part, per row) and then picks a single
entry. This rewrites it to `split_part(s, d, n)`, which short-circuits as soon
as it locates the n-th delimiter, eliminating the intermediate array and the
trailing-parts work.
The rewrite is semantics-preserving. The two forms differ only when the
string yields no n-th part: `element_at` returns NULL while `split_part` can
return `''`. To neutralize this, the rule only rewrites the ROOT of a top-level
filter conjunct (where NULL and false both drop the row) and is guarded to:
- EqualTo / InPredicate with a NON-EMPTY string-literal RHS (or an IN-list
of non-empty string literals), so a comparison against `''` yields false, not
true;
- a NON-EMPTY string-literal separator (an empty/column separator diverges);
- a NON-NEGATIVE int-literal index (negative back-counting uses rfind and
can land on a different boundary for self-overlapping multi-char separators).
It deliberately does NOT recurse into NOT / OR / CASE, where NULL and `''`
are no longer interchangeable.
### Release note
None
### Check List (For Author)
- [x] Test <!-- At least one of them must be included. -->
- [ ] Regression test
- [x] Unit Test
- [ ] Manual test (add detailed scripts or steps below)
- [ ] No need to test or manual test. Please explain why:
- [ ] Behavior changed:
- [ ] Does this need documentation?
### Check List (For Reviewer who merge this PR)
- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label
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