gengliangwang commented on a change in pull request #30894:
URL: https://github.com/apache/spark/pull/30894#discussion_r551435029
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
##########
@@ -175,20 +175,57 @@ abstract class UnaryNode extends LogicalPlan {
*/
protected def getAllValidConstraints(projectList: Seq[NamedExpression]):
ExpressionSet = {
var allConstraints = child.constraints
- projectList.foreach {
- case a @ Alias(l: Literal, _) =>
- allConstraints += EqualNullSafe(a.toAttribute, l)
- case a @ Alias(e, _) =>
- // For every alias in `projectList`, replace the reference in
constraints by its attribute.
- allConstraints ++= allConstraints.map(_ transform {
- case expr: Expression if expr.semanticEquals(e) =>
- a.toAttribute
+
+ // For each expression collect its aliases
+ val aliasMap = projectList.collect{
+ case alias @ Alias(expr, _) if !expr.foldable => (expr.canonicalized,
alias)
+ }.groupBy(_._1).mapValues(_.map(_._2))
+ val remainingExpressions = collection.mutable.Set(aliasMap.keySet.toSeq:
_*)
+
+ /**
+ * Filtering allConstraints between each iteration is necessary, because
+ * otherwise collecting valid constraints could in the worst case have
exponential
+ * time and memory complexity. Each replaced alias could double the number
of constraints,
+ * because we would keep both the original constraint and the one with
alias.
+ */
+ def shouldBeKept(expr: Expression): Boolean = {
+ expr.references.subsetOf(outputSet) ||
+ remainingExpressions.contains(expr.canonicalized) ||
+ (expr.children.nonEmpty && expr.children.forall(shouldBeKept))
+ }
+
+ // Replace expressions with aliases
+ for ((expr, aliases) <- aliasMap) {
+ allConstraints ++= allConstraints.flatMap(constraint => {
+ aliases.map(alias => {
+ constraint transform {
+ case e: Expression if e.semanticEquals(expr) =>
+ alias.toAttribute
+ }
})
- allConstraints += EqualNullSafe(e, a.toAttribute)
+ })
+
+ for { alias1 <- aliases; alias2 <- aliases } {
+ if (!alias1.fastEquals(alias2)) {
+ allConstraints += EqualNullSafe(alias1.toAttribute,
alias2.toAttribute)
+ }
+ }
+
+ remainingExpressions.remove(expr)
+ allConstraints = allConstraints.filter(shouldBeKept)
+ }
+
+ /**
+ We keep the child constraints and equality between original and aliased
attributes,
Review comment:
Could you show an example for why we should keep `child.constraints`?
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