github-actions[bot] commented on code in PR #64080:
URL: https://github.com/apache/doris/pull/64080#discussion_r3355749053
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fe/fe-core/src/main/java/org/apache/doris/nereids/types/ArrayType.java:
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@@ -57,6 +58,14 @@ public DataType getItemType() {
return itemType;
}
+ @Override
+ public boolean canSafetyCastTo(DataType target) {
+ if (target instanceof ArrayType) {
+ return itemType.canSafetyCastTo(((ArrayType) target).itemType);
+ }
+ return target instanceof CharacterType;
Review Comment:
This marks `ARRAY -> STRING/VARCHAR/CHAR` as distinctness-preserving, but
the BE string form for arrays is not injective. `DataTypeArraySerDe::to_string`
joins elements with `, ` and nested `DataTypeStringSerDeBase::to_string` only
wraps string elements in quotes without escaping embedded quotes. For example,
`array('a', 'b')` and `array('a" , "b')`-style values can serialize to the same
text once delimiters/quotes are embedded in a string element, while they are
distinct as arrays. With this predicate, `Project(CAST(array_col AS STRING))`
can be pushed below `UNION DISTINCT`, so the distinct runs on the stringified
values and collapses a row that the original plan would keep. Please do not
treat complex-to-character casts as safe unless the serialization is proven
injective; the same concern applies to the `MapType` and `StructType` `target
instanceof CharacterType` branches added in this PR.
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