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https://issues.apache.org/jira/browse/SPARK-25943?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Apache Spark reassigned SPARK-25943:
------------------------------------
Assignee: Apache Spark
> Corruption when writing data into a catalog table with a different struct
> schema
> --------------------------------------------------------------------------------
>
> Key: SPARK-25943
> URL: https://issues.apache.org/jira/browse/SPARK-25943
> Project: Spark
> Issue Type: Bug
> Components: Optimizer, SQL
> Affects Versions: 2.3.2, 2.4.1, 2.5.0, 3.0.0
> Reporter: James Baker
> Assignee: Apache Spark
> Priority: Major
>
> Suppose I have a catalog table with schema StructType(Seq(StructField("a",
> StructType(Seq(StructField("b", DataTypes.StringType), StructField("c",
> DataTypes.StringType))).
> Suppose I now try to append a record to it:
> {code:java}
> {"a": {"c": "data1", "b": "data2"}}
> {code}
> That record will actually be appended as:
> {code:java}
> {"a": {"b": "data1", "c": "data2"}}
> {code}
> which is obviously not close to what the user wanted or expected (for me it
> silently corrupted my data).
> It turns out that the user could provide a totally different record,
> {code:java}
> {"a": {"this column": "is totally different", "but": "the types match up"}}
> {code}
> and it'd still get written out, but as
> {code:java}
> {"a": {"b": "is totally different", "c": "the types match up"}}
> {code}
> This is because [in
> DDLPreprocessingUtils.castAndRenameOutput|https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/rules.scala#L500]
>
> [,|https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/rules.scala#L500],]
> Spark puts effort in to reordering column names in line with what the output
> expects, but merely casts any other types. This works nicely in a case where
> you try to e.g. write an int into a double field, but goes wrong on complex
> datatypes if the types match up but the field names do not.
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