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https://issues.apache.org/jira/browse/SPARK-44517?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17751325#comment-17751325
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Hive QA commented on SPARK-44517:
---------------------------------
User 'CodingCat' has created a pull request for this issue:
https://github.com/apache/spark/pull/42117
> first operator should respect the nullability of child expression as well as
> ignoreNulls option
> -----------------------------------------------------------------------------------------------
>
> Key: SPARK-44517
> URL: https://issues.apache.org/jira/browse/SPARK-44517
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 3.2.0, 3.2.1, 3.3.0, 3.2.2, 3.3.1, 3.2.3, 3.2.4, 3.3.2,
> 3.4.0, 3.4.1
> Reporter: Nan Zhu
> Priority: Major
>
> I found the following problem when using Spark recently:
>
> {code:java}
> // code placeholder
> import spark.implicits._
> val s = Seq((1.2, "s", 2.2)).toDF("v1", "v2", "v3")
> val schema = StructType(Seq(StructField("v1", DoubleType, nullable =
> false),StructField("v2", StringType, nullable = true),StructField("v3",
> DoubleType, nullable = false)))
> val df = spark.createDataFrame(s.rdd, schema)val inputDF =
> val inputDF = df.dropDuplicates("v3")
> spark.sql("CREATE TABLE local.db.table (\n v1 DOUBLE NOT NULL,\n v2 STRING,
> v3 DOUBLE NOT NULL)")
> inputDF.write.mode("overwrite").format("iceberg").save("local.db.table")
> {code}
>
>
> when I use the above code to write to iceberg (i guess Delta Lake will have
> the same problem) , I got very confusing exception
> {code:java}
> Exception in thread "main" java.lang.IllegalArgumentException: Cannot write
> incompatible dataset to table with schema:
> table
> { 1: v1: required double 2: v2: optional string 3: v3: required double}
> Provided schema:
> table { 1: v1: optional double 2: v2: optional string 3: v3: required
> double} {code}
> basically it complains that we have v1 as the nullable column in our
> `inputDF` above which is not allowed since we created table with the v1 as
> not nullable. The confusion comes from that, if we check the schema with
> printSchema() of inputDF, v1 is not nullable
> {noformat}
> root
> |-- v1: double (nullable = false)
> |-- v2: string (nullable = true)
> |-- v3: double (nullable = false){noformat}
> Clearly, something changed the v1's nullability unexpectedly!
>
> After some debugging I found that the key is that dropDuplicates("v3"). In
> optimization phase, we have ReplaceDeduplicateWithAggregate to replace the
> Deduplicate with aggregate on v3 and run first() over all other columns.
> However, first() operator has hard coded nullable as always "true" which is
> the source of changed nullability of v1
>
> this is a very confusing behavior of Spark, and probably no one really
> noticed as we do not care too much without the new table formats like delta
> lake and iceberg which can make nullability check correctly. Nowadays, we
> users adopt them more and more, this is surfaced up
>
>
>
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