zabetak commented on code in PR #6418:
URL: https://github.com/apache/hive/pull/6418#discussion_r3233225674
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ql/src/java/org/apache/hadoop/hive/ql/stats/StatsUtils.java:
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@@ -2112,7 +2115,7 @@ private static List<Long>
extractNDVGroupingColumns(List<ColStatistics> colStats
for (ColStatistics cs : colStats) {
if (cs != null) {
long ndv = cs.getCountDistint();
- if (cs.getNumNulls() > 0) {
+ if (cs.getNumNulls() > 0 && (ndv > 0 || cs.isConst())) {
ndv = StatsUtils.safeAdd(ndv, 1);
}
Review Comment:
If we know that a column is a constant then shouldn't `ndv = 1`? Why do we
want to do +1 ? Why do we care about the number of nulls?
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