Github user wzhfy commented on a diff in the pull request:
https://github.com/apache/spark/pull/19783#discussion_r155690722
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/FilterEstimation.scala
---
@@ -332,8 +332,41 @@ case class FilterEstimation(plan: Filter) extends
Logging {
colStatsMap.update(attr, newStats)
}
- Some(1.0 / BigDecimal(ndv))
- } else {
+ if (colStat.histogram.isEmpty) {
+ // returns 1/ndv if there is no histogram
+ Some(1.0 / BigDecimal(ndv))
+ } else {
+ // We compute filter selectivity using Histogram information.
+ // Here we traverse histogram bins to locate the range of bins the
literal values falls
+ // into. For skewed distribution, a literal value can occupy
multiple bins.
+ val hgmBins = colStat.histogram.get.bins
+ val datum = EstimationUtils.toDecimal(literal.value,
literal.dataType).toDouble
--- End diff --
yes, I'll refactor this part.
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