yujun777 commented on code in PR #62742:
URL: https://github.com/apache/doris/pull/62742#discussion_r3356110310
##########
fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/AddProjectForVolatileExpression.java:
##########
@@ -269,6 +271,85 @@ public <T extends Expression> Optional<Pair<List<T>,
LogicalProject<Plan>>> rewr
return Optional.of(Pair.of(newTargetsBuilder.build(), new
LogicalProject<>(projects, plan.child(0))));
}
+ private Optional<JoinRewriteResult>
rewriteJoinExpressions(LogicalJoin<Plan, Plan> join,
+ Collection<Expression> targets) {
+ Map<Expression, Integer> volatileExpressionCounter =
Maps.newLinkedHashMap();
+ Map<Expression, Set<Slot>> volatileExpressionSlots =
Maps.newLinkedHashMap();
+ for (Expression target : targets) {
+ target.foreach(e -> {
+ Expression expr = (Expression) e;
+ if (expr.isVolatile()) {
+ volatileExpressionCounter.merge(expr, 1, Integer::sum);
+ Set<Slot> inputSlots = expr.getInputSlots();
+ volatileExpressionSlots
+ .computeIfAbsent(expr, ignored ->
Sets.newLinkedHashSet())
+ .addAll(inputSlots.isEmpty() ?
target.getInputSlots() : inputSlots);
+ }
+ });
+ }
+
+ ImmutableList.Builder<NamedExpression> leftAliases =
ImmutableList.builder();
+ ImmutableList.Builder<NamedExpression> rightAliases =
ImmutableList.builder();
+ Map<Expression, Slot> replaceMap = Maps.newHashMap();
+ Set<Slot> leftOutputSet = join.left().getOutputSet();
+ Set<Slot> rightOutputSet = join.right().getOutputSet();
+ for (Entry<Expression, Integer> entry :
volatileExpressionCounter.entrySet()) {
+ if (entry.getValue() <= 1) {
+ continue;
Review Comment:
I think this is the less-bad behavior under Doris's current join/project
split. A cannot represent a per-pair project for a volatile expression, so if
the same volatile node appears multiple times after rewrites like expansion,
leaving it in the join means it will be re-evaluated independently for each
occurrence and can diverge within the same predicate. By materializing it into
one child project, we at least force repeated references to share a single
value, which preserves the one-value-per-expression property that the original
predicate needs. This is not fully equivalent to the join-pair semantics, but
it is strictly better than keeping the duplicated volatile expression on the
join and letting it be re-sampled separately.
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