liyafan82 commented on a change in pull request #2330:
URL: https://github.com/apache/calcite/pull/2330#discussion_r562488708
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File path: core/src/main/java/org/apache/calcite/util/RangeSets.java
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@@ -105,6 +110,45 @@ private RangeSets() {}
return 0;
}
+ /**
+ * Estimates the number of distinct values for a range (if possible).
+ * A null is returned if the number of distinct values is infinity or
unknown.
+ */
+ public static <C extends Comparable<C>> @Nullable Double numDistinctVals(
+ Range<C> range, RelDataType type) {
+ if (RangeSets.isPoint(range)) {
+ return 1.0;
Review comment:
Returning null means we do not have an estimation, or equivalently, the
number of distinct values is infinity.
When the range is a point (e.g. `x = 1`), we estimate that there is only one
distinct value, which is likely to be true in practice.
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