Jiri Humpolicek created SPARK-34638:
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             Summary: Spark SQL reads unnecessary nested fields (another type 
of pruning case)
                 Key: SPARK-34638
                 URL: https://issues.apache.org/jira/browse/SPARK-34638
             Project: Spark
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 3.1.1
            Reporter: Jiri Humpolicek


Based on this [SPARK-29721|https://issues.apache.org/jira/browse/SPARK-29721] I 
found another nested fields pruning case.

Example:
1) Loading data

{code:scala}
val jsonStr = """{
 "items": [
   {"itemId": 1, "itemData": "a"},
   {"itemId": 2, "itemData": "b"}
 ]
}"""
val df = spark.read.json(Seq(jsonStr).toDS)
df.write.format("parquet").mode("overwrite").saveAsTable("persisted")
{code}

2) read query with explain

{code:scala}
val read = spark.table("persisted")
spark.conf.set("spark.sql.optimizer.nestedSchemaPruning.enabled", true)

read.select(explode($"items").as('item)).select($"item.itemId").explain(true)
// ReadSchema: struct<items:array<struct<itemData:string,itemId:bigint>>>
{code}




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