ILuffZhe commented on code in PR #4099:
URL: https://github.com/apache/calcite/pull/4099#discussion_r1891123328
##########
core/src/main/java/org/apache/calcite/rel/metadata/RelMdUtil.java:
##########
@@ -210,6 +210,18 @@ public static boolean
areColumnsDefinitelyUnique(RelMetadataQuery mq,
return b != null && b;
}
+ public static boolean isRelDefinitelyEmpty(RelMetadataQuery mq,
+ RelNode rel) {
+ Boolean b = mq.isEmpty(rel);
+ return b != null && b;
+ }
+
+ public static boolean isRelDefinitelyNotEmpty(RelMetadataQuery mq,
Review Comment:
Can this method be replaced by "!isRelDefinitelyEmpty"?
##########
core/src/main/java/org/apache/calcite/tools/RelBuilder.java:
##########
@@ -2678,10 +2679,7 @@ private boolean alreadyUnique(List<AggCallPlus>
aggCallList,
List<RexNode> extraNodes) {
final RelMetadataQuery mq = peek().getCluster().getMetadataQuery();
if (aggCallList.isEmpty() && groupSet.isEmpty()) {
- final Double minRowCount = mq.getMinRowCount(peek());
- if (minRowCount == null || minRowCount < 1d) {
- // We can't remove "GROUP BY ()" if there's a chance the rel could be
Review Comment:
Why delete the doc?
##########
core/src/main/java/org/apache/calcite/rel/metadata/RelMetadataQuery.java:
##########
@@ -305,6 +305,26 @@ public static RelMetadataQuery instance() {
}
}
+ /**
+ * Returns whether the return rows of a given relational expression are
empty.
Review Comment:
nit: "a given relational expression is empty"
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