cloud-fan commented on code in PR #40865:
URL: https://github.com/apache/spark/pull/40865#discussion_r1177426150
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/subquery.scala:
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@@ -459,7 +459,7 @@ object RewriteCorrelatedScalarSubquery extends
Rule[LogicalPlan] with AliasHelpe
case alias @ Alias(_: AttributeReference, _) =>
(alias.exprId, Literal.create(null, alias.dataType))
case alias @ Alias(l: Literal, _) =>
- (alias.exprId, l.copy(value = null))
+ (alias.exprId, l)
Review Comment:
I think this one-line change is all we need. Count bug does not apply to the
count function only, but all expressions in Aggregate that return non-null
value for empty input. This includes all constant values.
Assume there are two table `t1(c1 int)`, `t2(c2 int)`. `t1` has two rows (1,
2), `t2` has two rows (1,3)
```
scala> sql("select (select f from (select false as f, max(c1) from t1 where
c1 = c2)) from t2").show
+------------------+
|scalarsubquery(c2)|
+------------------+
| false|
| NULL|
+------------------+
```
The result is wrong and it should be false, false
`select f from (select false as f, max(c1) from t1 where c1 = c2)` is to
build a global aggregate that has no aggregate function. If SQL syntax supports
group by no column, then we can simply write `select false as f from t1 group
by () where c1 = c2`
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