cloud-fan commented on a change in pull request #32301:
URL: https://github.com/apache/spark/pull/32301#discussion_r620104642
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
##########
@@ -23,78 +23,149 @@ 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(_gen_alias_2#2, _gen_alias_3#3) AS concat_ws(s.a,
s.b)#1]
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- Project [s#0.a AS _gen_alias_2#2, s#0.b AS _gen_alias_3#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 [_gen_alias_2#2 AS s.a#1]
+ * +- Filter (length(_gen_alias_3#3) > 2)
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- Project [s#0.a AS _gen_alias_2#2, s#0.b AS _gen_alias_3#3]
+ * +- LocalRelation <empty>, [s#0]
+ *
+ * Example 3: Nested columns in nested columns
Review comment:
I think we do support nested column pruning with any levels. The example
is more about "Nested fields with parent field being referenced".
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
For queries about this service, please contact Infrastructure at:
us...@infra.apache.org
---------------------------------------------------------------------
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
