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_r367372431
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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@@ -757,3 +757,45 @@ object CombineConcats extends Rule[LogicalPlan] {
flattenConcats(concat)
}
}
+
+/**
+ * Removes unnecessary null checks for If/CaseWhen conditions
+ * with NullIntolerant expressions.
+ */
+object RemoveRedundantNullChecks extends Rule[LogicalPlan] {
+ /**
+ * @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 isRedundant(
+ ifNullExpr: Expression,
+ ifNotNullExpr: Expression,
+ checkedExpr: Expression): Boolean = {
+ (ifNullExpr == checkedExpr || ifNullExpr == Literal.create(null,
checkedExpr.dataType)) &&
+ ifNotNullExpr.isInstanceOf[NullIntolerant] &&
+ ifNotNullExpr.children.contains(checkedExpr)
+ }
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transformAllExpressions {
+ case i @ If(predicate, trueValue, falseValue) => predicate match {
Review comment:
The `NullPropagation` rule simplifies expressions to literals. But i feel
that my pr is covering slightly different case. Here the expression that is
being null-checked is in general not `Literal` and can not be converted to
`Literal` (in general).
However I can also see that the logic of my rule can be moved to
`SimplifyConditionals`, so I can move it there if this is the preferred way.
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