github-actions[bot] commented on code in PR #67718:
URL: https://github.com/apache/doris/pull/67718#discussion_r4043272241
##########
fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/AccessPathExpressionCollector.java:
##########
@@ -344,6 +345,21 @@ public Void visitCast(Cast cast, CollectorContext context)
{
);
}
+ @Override
+ public Void visitTryCast(TryCast tryCast, CollectorContext context) {
+ // TRY_CAST semantics cover the WHOLE value: for a composite type any
element
+ // conversion failure makes the entire cast NULL. Narrowing the
read/type down to
+ // only the fields an outer expression accesses would drop the
conversion attempts
+ // of the other fields and silently change the result (e.g.
element_at(try_cast(s as
+ // struct<a:int,b:int>), 'a') must still yield NULL when only field b
is unparsable,
+ // even though field a alone converts fine). Plain Cast over nested
types is pruned
+ // field-by-field on purpose, a TryCast never is: read the whole child
value and keep
+ // the cast identity and target type intact.
+ return tryCast.child(0).accept(this,
+ new CollectorContext(context.statementContext,
context.bottomFilter)
+ );
Review Comment:
Preserve `TryCast` when a derived child is rebuilt. For example:
```text
Project element_at(
TryCast(element_at(wrapper, 'inner') AS struct<good:int,bad:int>),
'good')
Scan wrapper struct<inner:struct<good:string,bad:string>,unused:int>
```
The fresh context here records `[wrapper, inner]`, so pruning can remove
`wrapper.unused` while retaining the complete `inner` value. That changes the
wrapper slot and rebuilds the inner `ElementAt`; `SlotTypeReplacer.rewriteCast`
then sees a changed child and unconditionally returns `new Cast(...)`, erasing
`TryCast`. With strict casting and `inner.bad = 'bad'`, the rewritten
expression raises instead of returning NULL for the whole try-cast row. Please
preserve the dynamic cast kind when rebuilding (for example through
`withChildren`/`withTargetType` or explicit `TryCast` handling), and add a
derived-child regression that asserts the physical expression and result
semantics.
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