Github user chenghao-intel commented on a diff in the pull request:
https://github.com/apache/spark/pull/4892#discussion_r25859379
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
---
@@ -192,14 +193,17 @@ abstract class LogicalPlan extends
QueryPlan[LogicalPlan] with Logging {
// One match, but we also need to extract the requested nested field.
case Seq((a, nestedFields)) =>
- // The foldLeft adds UnresolvedGetField for every remaining parts
of the name,
- // and aliased it with the last part of the name.
- // For example, consider name "a.b.c", where "a" is resolved to an
existing attribute.
- // Then this will add UnresolvedGetField("b") and
UnresolvedGetField("c"), and alias
- // the final expression as "c".
- val fieldExprs = nestedFields.foldLeft(a:
Expression)(UnresolvedGetField)
- val aliasName = nestedFields.last
- Some(Alias(fieldExprs, aliasName)())
+ // The foldLeft will resolve all of the nested data type, to get
its attributes.
+ val fieldExprs = nestedFields.foldLeft(a: Expression) { case (e,
fieldName) =>
+ resolveGetField(e, fieldName, resolver)
+ }
+
+ // TODO the alias name is quite tricky to me, set it to _col1,
_col2.. ?
+ // Set it as original attribute name like "a.b.c" seems still
confusing,
+ // and we may never reference this column by its name (with "."),
except
+ // people write SQL like: SELECT a.b.c as newCol FROM nestedTable,
which
+ // explicitly specifying the alias name for the output column
+ Some(Alias(fieldExprs, name)())
--- End diff --
I am not so sure how Hive handle that, but it can not be `c`; otherwise it
may cause reference arbitrary for its parent logical plan.
e.g.
Assume we have table `tbl` with schema Struct<a: Struct<b:Int, c: Int>, b:
int>
```
SELECT b FROM (SELECT a.b, b FROM tbl)
```
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