[GitHub] [spark] maropu commented on a change in pull request #29900: [SPARK-32958][SQL] Prune unnecessary columns from JsonToStructs

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

maropu commented on a change in pull request #29900:
URL: https://github.com/apache/spark/pull/29900#discussion_r498056679



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/OptimizeJsonExprs.scala
##########
@@ -38,6 +43,15 @@ object OptimizeJsonExprs extends Rule[LogicalPlan] {
         // so `JsonToStructs` might throw error in runtime. Thus we cannot optimize
         // this case similarly.
         child
+
+      case g @ GetStructField(jsonToStructs: JsonToStructs, ordinal, _) =>
+        val prunedSchema = StructType(Seq(jsonToStructs.schema.asInstanceOf[StructType](ordinal)))

Review comment:
       nit: we might be able to filter out a schema.length=1 case:
   ```
         case g @ GetStructField(jts @ JsonToStructs(schema: StructType, _, _, _), ordinal, _)
             if schema.length > 1 =>
           val prunedSchema = StructType(Seq(schema(ordinal)))
   ```

##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/OptimizeJsonExprs.scala
##########
@@ -38,6 +43,15 @@ object OptimizeJsonExprs extends Rule[LogicalPlan] {
         // so `JsonToStructs` might throw error in runtime. Thus we cannot optimize
         // this case similarly.
         child
+
+      case g @ GetStructField(jsonToStructs: JsonToStructs, ordinal, _) =>
+        val prunedSchema = StructType(Seq(jsonToStructs.schema.asInstanceOf[StructType](ordinal)))
+        g.copy(child = jsonToStructs.copy(schema = prunedSchema), ordinal = 0)
+
+      case g @ GetArrayStructFields(jsonToStructs: JsonToStructs, _, _, _, _) =>

Review comment:
       ditto




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