davidvrba commented on a change in pull request #27231: [SPARK-28478][SQL]
Remove redundant null checks
URL: https://github.com/apache/spark/pull/27231#discussion_r376882451
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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@@ -434,6 +434,27 @@ object SimplifyConditionals extends Rule[LogicalPlan]
with PredicateHelper {
case _ => false
}
+ /**
+ * Condition for redundant null check based on intolerant expressions.
+ * @param ifNullExpr expression that takes place if checkedExpr is null
+ * @param ifNotNullExpr expression that takes place if checkedExpr is not
null
+ * @param checkedExpr expression that is checked for null value
+ */
+ private def isRedundantNullCheck(
+ ifNullExpr: Expression,
+ ifNotNullExpr: Expression,
+ checkedExpr: Expression): Boolean = {
+ val isNullIntolerant = ifNotNullExpr.find { x =>
+ !x.isInstanceOf[NullIntolerant] && x.find(e =>
e.semanticEquals(checkedExpr)).nonEmpty
Review comment:
I agree that the committed code is not very intuitive so i can think of this
way which seems to be more readable (added also some comments):
```
private def isRedundantNullCheck(
ifNullExpr: Expression,
ifNotNullExpr: Expression,
checkedExpr: Expression): Boolean = {
// checks if expr is null-intolerant with respect to checkedExpr
def isNullIntolerant(expr: Expression): Boolean = expr match {
case e: NullIntolerant => e.children.forall(isNullIntolerant)
// if some child is null-tolerant but the checkedEpxr is not in its
subtree
// we can still consider the whole expr as null-intolerant
// with respect to checkedExpr
case e if e.find(x => x.semanticEquals(checkedExpr)).isEmpty => true
case _ => false
}
isNullIntolerant(ifNotNullExpr) && {
(ifNullExpr.semanticEquals(checkedExpr) ||
(ifNullExpr.foldable && ifNullExpr.eval() == null)) &&
// we still need to make sure that checkedExpr is inside ifNotNullExpr
ifNotNullExpr.find(x => x.semanticEquals(checkedExpr)).nonEmpty
}
}
```
But not sure if this is what you had in mind when suggesting to split the
condition. Can you think of a better way how to compose this?
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