morrySnow opened a new pull request, #67803:
URL: https://github.com/apache/doris/pull/67803
### What problem does this PR solve?
Problem Summary:
When nested-column pruning was disabled, a multi-level VARIANT access could
return different values from the regular and constant branches of a `UNION
ALL`. For example, with `{"a":{"b":1},"b":{"a":2}}`, selecting `c['a']['b']`
returned `1` from the table branch but `2` from the constant branch.
The pruning context stores sub-paths in canonical root-to-leaf order, such
as `[a, b]`. The UNION constant-expression rewrite and the project pushdown
rewrite rebuilt nested `ElementAt` expressions by iterating those paths
backwards, producing `c['b']['a']`.
This change centralizes construction of nested `ElementAt` expressions and
applies each canonical sub-path from root to leaf. It uses the same helper for
UNION constant expressions and projected VARIANT expressions so extraction and
reconstruction share one order contract.
The regression test reproduces the UNION result mismatch with nested-column
pruning disabled, covers the projected-expression path, and verifies the
enabled-pruning control case.
### Release note
Fix incorrect values for multi-level VARIANT sub-paths in UNION ALL constant
branches.
### Check List (For Author)
- Test:
- Unit Test: `PruneNestedColumnTest` (62 tests)
- Regression Test: `variant_p0/test_variant_sub_path_order`
- Full FE build
- Behavior changed: Yes. Multi-level VARIANT sub-paths now preserve SQL
access order across rewritten branches.
- Does this need documentation: No
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