darpan-e6 commented on code in PR #4970:
URL: https://github.com/apache/calcite/pull/4970#discussion_r3315311244
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core/src/main/java/org/apache/calcite/plan/RelOptUtil.java:
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@@ -3346,6 +3346,21 @@ public static List<RexNode> pushPastProject(List<?
extends RexNode> nodes,
// function? Possibly. But it's invalid SQL, so don't go there.
return null;
}
+ // [CALCITE-7551] Refuse to merge if it would duplicate a
+ // non-deterministic expression (e.g. RAND()).
+ final List<RexNode> bottom = project.getProjects();
+ final int[] refs = new int[bottom.size()];
+ new RexVisitorImpl<Void>(true) {
+ @Override public Void visitInputRef(RexInputRef ref) {
+ refs[ref.getIndex()]++;
+ return null;
+ }
+ }.visitEach(nodes);
+ for (int i = 0; i < refs.length; i++) {
Review Comment:
As far as I understand, CURRENT_TIMESTAMP is actually different than
non-deterministic functions like RAND().
1. Non-deterministic function: it may return different values for every
evaluations.
1.1 Returns false to `isDeterministic()`.
1.2 Returns false to `isDynamicFunction()`.
2. Dynamic Function: It will return same value at every call site within one
statement; can differ across executions
2.1 Returns true to `isDeterministic()`.
2.2 Returns true to `isDynamicFunction()`.
And this path only blocks when we get `isDeterministic()` method response as
false. Dynamic functions like `CURRENT_TIMESTAMP` can be duplicated and
actually it is safe to duplicate them.
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