zabetak commented on code in PR #5795:
URL: https://github.com/apache/hive/pull/5795#discussion_r2068653594
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ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/SearchTransformer.java:
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@@ -128,8 +132,23 @@ public Shuttle(final RexBuilder rexBuilder) {
} else {
return call;
}
+ case IS_NULL:
+ case IS_NOT_NULL:
+ case CASE:
+ case COALESCE:
+ // Everything below must be transformed with the UNKNOWN handler
Review Comment:
There are some operators with special semantics that we need to retain the
3-valued logic even if we are inside the `WHERE` clause.
Example: `COALESCE(SEARCH(...), true)`
1. If SEARCH -> true then COALESCE -> true
2. If SEARCH -> false then COALESCE -> false
3. If SEARCH -> null then COALESCE -> true
If we consider `unknownAsFalse` inside the COALESCE then we will incorrectly
drop the `IS NOT NULL` predicate during the expansion and the COALESCE will
fall into the third case returning `true` instead of `false`.
Basically, if the SEARCH is below/inside an operator that is sensitive to
null values we cannot safely perform the simplification.
Note that `RexSimplify` also changes the default unknown semantics for
certain operators (see `simplifyIs2`, `simplifyCoalesce`, etc.).
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