englefly opened a new pull request, #67718:
URL: https://github.com/apache/doris/pull/67718
### What problem does this PR solve?
Issue Number: N/A
Problem Summary:
Nested column pruning rewrites a struct-field access over `TRY_CAST` into a
plain `CAST` and narrows both the read and the conversion to the accessed
field, dropping the whole-value semantics of TRY_CAST.
Reproduction (single FE/BE, `enable_strict_cast=true`):
```sql
CREATE TABLE t (id INT, s STRUCT<a:STRING,b:STRING> NULL)
DISTRIBUTED BY HASH(id) BUCKETS 1
PROPERTIES ("replication_num"="1");
INSERT INTO t VALUES
(1,named_struct('a','bad','b','2')),
(2,named_struct('a','10','b','bad')),(3,NULL);
-- with nested column pruning enabled (default)
SELECT id, TRY_CAST(s AS STRUCT<a:INT,b:INT>)['a'] AS a_i FROM t;
```
- id=2: `b='bad'` makes the whole-struct TRY_CAST fail and should yield
NULL, but pruning drops field `b`, the conversion "succeeds" on `a='10'`, and
the query returns 10.
- id=1: the rebuilt plain CAST (instead of TRY_CAST) throws
`[INVALID_ARGUMENT] parse number fail, string: 'bad'` under
`enable_strict_cast=true` instead of returning NULL.
- Root cause: `AccessPathExpressionCollector.visitCast` handles `TryCast` (a
`Cast` subclass) like a plain cast and translates the narrowed nested access
path through it, so `SlotTypeReplacer.rewriteCast` later rebuilds the
expression as `new Cast(...)` with a pruned target type.
Fix: do not translate a narrowed nested access path through a `TRY_CAST`;
the collector then falls back to reading the whole child value, so the struct
keeps all fields and the expression keeps its TRY_CAST identity and full target
type. Field-by-field pruning of plain `CAST` over nested types is unchanged.
### Release note
None
### Check List (For Author)
- Test:
- [x] Unit Test:
`PruneNestedColumnTest#testTryCastNotPrunedThroughFieldAccess` (whole class: 62
tests pass)
- [x] Manual test (detailed steps): reproduced the SQL above end-to-end
on a local FE+BE cluster built from this change. With
`enable_prune_nested_column` on and off all three rows return NULL (no 10, no
exception under `enable_strict_cast=true`); `EXPLAIN VERBOSE` keeps
`element_at(TRY_CAST(s AS struct<a:int,b:int>), 'a')` with `all access paths:
[s]`, while plain `CAST` over the same struct is still pruned to
`struct<a:int>` with `[s.a]`.
- Behavior changed:
- [x] Yes: enabling/disabling nested column pruning no longer changes
TRY_CAST results or error semantics.
- Does this need documentation?
- [x] No.
### 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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