xiedeyantu commented on code in PR #4515:
URL: https://github.com/apache/calcite/pull/4515#discussion_r2311759566
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core/src/main/java/org/apache/calcite/rel/rules/SortJoinTransposeRule.java:
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@@ -102,10 +101,7 @@ public SortJoinTransposeRule(Class<? extends Sort>
sortClass,
return false;
}
}
- }
- if (sort.offset != null
Review Comment:
JOIN is an unordered operation, even if its left and right child nodes have
been sorted earlier. For example, in
"SORT(offset=2)-LEFTJOIN", even if the join keys of the right table are
unique, it is not safe to push the OFFSET down to the left table. This is
because Calcite's current JOIN computation logic cannot guarantee that
performing the offset first and then computing the JOIN yields the same result
as computing the JOIN first and then applying the offset. The same logic
applies to other database systems as well. Therefore, prohibiting the pushdown
of OFFSET is a safe equivalent transformation. Hence, the PR directly disallows
the pushdown of OFFSET.
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