dongjoon-hyun commented on a change in pull request #24158: [SPARK-26847][SQL]
Pruning nested serializers from object serializers: MapType support
URL: https://github.com/apache/spark/pull/24158#discussion_r268037271
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/objects.scala
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@@ -132,49 +130,74 @@ object ObjectSerializerPruning extends Rule[LogicalPlan]
{
fields.map(f => collectStructType(f.dataType, structs))
case ArrayType(elementType, _) =>
collectStructType(elementType, structs)
+ case MapType(_, valueType, _) =>
+ // Because we can't select a field from struct in key, so we skip key
type.
Review comment:
Technically, `map_keys` returns key arrays and we can select fields from the
keys.
```scala
scala> sql("select keys, keys.a from (select map_keys(map(named_struct('a',
'key1'), 1, named_struct('a', 'key2'), 2)) keys)").show
+----------------+------------+
| keys| a|
+----------------+------------+
|[[key1], [key2]]|[key1, key2]|
+----------------+------------+
```
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