chunweilei commented on a change in pull request #2355:
URL: https://github.com/apache/calcite/pull/2355#discussion_r589132188
##########
File path:
core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistinctRowCount.java
##########
@@ -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:
What would it return without your change?
##########
File path: core/src/main/java/org/apache/calcite/rel/core/Project.java
##########
@@ -442,6 +443,19 @@ public boolean isMapping() {
return true;
}
+ /**
+ * Given some columns, gets the non-constant ones.
+ */
+ public ImmutableBitSet getNonConstColumns(ImmutableBitSet columns) {
+ ImmutableBitSet.Builder nonConstCols = ImmutableBitSet.builder();
+ for (int col : columns) {
+ if (!RexUtil.isLiteral(getProjects().get(col), true)) {
+ nonConstCols.set(col);
+ }
+ }
Review comment:
Would it better to put this method to RexUtils for being reused?
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