[GitHub] [spark] viirya commented on a change in pull request #29092: [SPARK-32295][SQL] Add not null and size > 0 filters before inner explode/inline to benefit from predicate pushdown

[GitBox <gi...@apache.org>]

viirya commented on a change in pull request #29092:
URL: https://github.com/apache/spark/pull/29092#discussion_r504079357



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -868,6 +866,41 @@ object TransposeWindow extends Rule[LogicalPlan] {
   }
 }
 
+/**
+ * Infers filters from [[Generate]], such that rows that would have been removed
+ * by this [[Generate]] can be removed earlier - before joins and in data sources.
+ */
+object InferFiltersFromGenerate extends Rule[LogicalPlan] {
+  def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
+    // This rule does not infer filters from foldable expressions to avoid constant filters
+    // like 'size([1, 2, 3]) > 0'. These do not show up in child's constraints and
+    // then the idempotence will break.
+    case generate @ Generate(e, _, _, _, _, _)
+      if !e.deterministic || e.children.forall(_.foldable) => generate
+
+    case generate @ Generate(g, _, false, _, _, _) if canInferFilters(g) =>
+      // Exclude child's constraints to guarantee idempotency
+      val inferredFilters = ExpressionSet(
+        Seq(
+          GreaterThan(Size(g.children.head), Literal(0)),

Review comment:
       This can be useful to filter rows before join, but can we pushdown `Size` expression to datasource?




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