englefly commented on code in PR #17916:
URL: https://github.com/apache/doris/pull/17916#discussion_r1141245299
##########
fe/fe-core/src/main/java/org/apache/doris/nereids/stats/JoinEstimation.java:
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@@ -39,9 +39,9 @@ private static Statistics estimateInnerJoin(Statistics
crossJoinStats, List<Expr
.sorted((a, b) -> {
double sub = a.second - b.second;
if (sub > 0) {
- return -1;
- } else if (sub < 0) {
return 1;
+ } else if (sub < 0) {
+ return -1;
Review Comment:
because this formula
```
for (int i = 0; i < sortedJoinConditions.size(); i++) {
sel *= Math.pow(sortedJoinConditions.get(i).second, 1 /
Math.pow(2, i));
}
```
sel=sel0 * sel1^(1/2) * ...
if sel0 > sel1, we have sel>sel0, but sel>sel1 is not always hold.
suppose we have filter `(a=b) and (c=d)`
sel1: selectivity of (a=b), sel1=0.5
sel2: selectivity of (c=d), sel2=0.04
sel= 0.5 * 0.2 = 0.25
then sel > sel2. this is wrong
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