cloud-fan commented on a change in pull request #32301:
URL: https://github.com/apache/spark/pull/32301#discussion_r638909542
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
##########
@@ -17,71 +17,155 @@
package org.apache.spark.sql.catalyst.optimizer
+import scala.collection.mutable
+
import org.apache.spark.sql.catalyst.expressions._
import org.apache.spark.sql.catalyst.plans.logical._
import org.apache.spark.sql.internal.SQLConf
import org.apache.spark.sql.types._
/**
- * This aims to handle a nested column aliasing pattern inside the
`ColumnPruning` optimizer rule.
- * If a project or its child references to nested fields, and not all the
fields
- * in a nested attribute are used, we can substitute them by alias attributes;
then a project
- * of the nested fields as aliases on the children of the child will be
created.
+ * This aims to handle a nested column aliasing pattern inside the
[[ColumnPruning]] optimizer rule.
+ * If:
+ * - A [[Project]] or its child references nested fields
+ * - Not all of the fields in a nested attribute are used
+ * Then:
+ * - Substitute the nested field references with alias attributes
+ * - Add grandchild [[Project]]s transforming the nested fields to aliases
+ *
+ * Example 1: Project
+ * ------------------
+ * Before:
+ * +- Project [concat_ws(s#0.a, s#0.b) AS concat_ws(s.a, s.b)#1]
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- LocalRelation <empty>, [s#0]
+ * After:
+ * +- Project [concat_ws(_extract_a#2, _extract_b#3) AS concat_ws(s.a, s.b)#1]
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- Project [s#0.a AS _extract_a#2, s#0.b AS _extract_b#3]
+ * +- LocalRelation <empty>, [s#0]
+ *
+ * Example 2: Project above Filter
+ * -------------------------------
+ * Before:
+ * +- Project [s#0.a AS s.a#1]
+ * +- Filter (length(s#0.b) > 2)
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- LocalRelation <empty>, [s#0]
+ * After:
+ * +- Project [_extract_a#2 AS s.a#1]
+ * +- Filter (length(_extract_b#3) > 2)
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- Project [s#0.a AS _extract_a#2, s#0.b AS _extract_b#3]
+ * +- LocalRelation <empty>, [s#0]
+ *
+ * Example 3: Nested fields with referenced parents
+ * ------------------------------------------------
+ * Before:
+ * +- Project [s#0.a AS s.a#1, s#0.a.a1 AS s.a.a1#2]
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- LocalRelation <empty>, [s#0]
+ * After:
+ * +- Project [_extract_a#3 AS s.a#1, _extract_a#3.name AS s.a.a1#2]
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- Project [s#0.a AS _extract_a#3]
+ * +- LocalRelation <empty>, [s#0]
+ *
+ * The schema of the datasource relation will be pruned in the
[[SchemaPruning]] optimizer rule.
*/
object NestedColumnAliasing {
def unapply(plan: LogicalPlan): Option[LogicalPlan] = plan match {
/**
* This pattern is needed to support [[Filter]] plan cases like
- * [[Project]]->[[Filter]]->listed plan in `canProjectPushThrough` (e.g.,
[[Window]]).
- * The reason why we don't simply add [[Filter]] in
`canProjectPushThrough` is that
+ * [[Project]]->[[Filter]]->listed plan in [[canProjectPushThrough]]
(e.g., [[Window]]).
+ * The reason why we don't simply add [[Filter]] in
[[canProjectPushThrough]] is that
* the optimizer can hit an infinite loop during the
[[PushDownPredicates]] rule.
*/
- case Project(projectList, Filter(condition, child))
- if SQLConf.get.nestedSchemaPruningEnabled &&
canProjectPushThrough(child) =>
Review comment:
nit: I think the previous code is better that put `if` in this line.
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