liyafan82 commented on a change in pull request #2355:
URL: https://github.com/apache/calcite/pull/2355#discussion_r589917976
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File path:
core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistinctRowCount.java
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@@ -227,6 +227,21 @@ public Double getDistinctRowCount(Values rel,
RelMetadataQuery mq,
return 1D;
}
}
+
+ // try to remove const columns from the group keys, as they do not
+ // affect the distinct row count
+ ImmutableBitSet nonConstCols = rel.getNonConstColumns(groupKey);
+ if (nonConstCols.cardinality() == 0) {
+ // all columns are constants, the distinct row count should be 1
+ return 1D;
+ }
+
+ if (nonConstCols.cardinality() < groupKey.cardinality()) {
+ // some const columns can be removed, call the method recursively
+ // with the trimmed columns
+ return getDistinctRowCount(rel, mq, nonConstCols, predicate);
+ }
Review comment:
It would return the of distinct row count from the input, which is null
for most cases.
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