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https://issues.apache.org/jira/browse/SPARK-18859?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16075432#comment-16075432
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Anton Okolnychyi commented on SPARK-18859:
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I took a look at this issue and seems this cannot be fixed on the Spark side.
{{JdbcUtils#getSchema}} is responsible for identifying the schema in this case.
Under the hood, it just uses the metadata from a {{ResultSet}} to create a
{{Catalyst}} schema. The Optimizer is not involved in the schema extraction,
everything is based on the {{ResultSet}} metadata. Therefore, this issue is
only reproducible if the user specifies a query as the "dbtable" JDBC option.
> Catalyst codegen does not mark column as nullable when it should. Causes NPE
> ----------------------------------------------------------------------------
>
> Key: SPARK-18859
> URL: https://issues.apache.org/jira/browse/SPARK-18859
> Project: Spark
> Issue Type: Bug
> Components: Optimizer, SQL
> Affects Versions: 2.0.2
> Reporter: Mykhailo Osypov
> Priority: Critical
>
> When joining two tables via LEFT JOIN, columns in right table may be NULLs,
> however catalyst codegen cannot recognize it.
> Example:
> {code:title=schema.sql|borderStyle=solid}
> create table masterdata.testtable(
> id int not null,
> age int
> );
> create table masterdata.jointable(
> id int not null,
> name text not null
> );
> {code}
> {code:title=query_to_select.sql|borderStyle=solid}
> (select t.id, t.age, j.name from masterdata.testtable t left join
> masterdata.jointable j on t.id = j.id) as testtable;
> {code}
> {code:title=master code|borderStyle=solid}
> val df = sqlContext
> .read
> .format("jdbc")
> .option("dbTable", "query to select")
> ....
> .load
> //df generated schema
> /*
> root
> |-- id: integer (nullable = false)
> |-- age: integer (nullable = true)
> |-- name: string (nullable = false)
> */
> {code}
> {code:title=Codegen|borderStyle=solid}
> /* 038 */ scan_rowWriter.write(0, scan_value);
> /* 039 */
> /* 040 */ if (scan_isNull1) {
> /* 041 */ scan_rowWriter.setNullAt(1);
> /* 042 */ } else {
> /* 043 */ scan_rowWriter.write(1, scan_value1);
> /* 044 */ }
> /* 045 */
> /* 046 */ scan_rowWriter.write(2, scan_value2);
> {code}
> Since *j.name* is from right table of *left join* query, it may be null.
> However generated schema doesn't think so (probably because it defined as
> *name text not null*)
> {code:title=StackTrace|borderStyle=solid}
> java.lang.NullPointerException
> at
> org.apache.spark.sql.catalyst.expressions.codegen.UnsafeRowWriter.write(UnsafeRowWriter.java:210)
> at
> org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIterator.processNext(Unknown
> Source)
> at
> org.apache.spark.sql.execution.BufferedRowIterator.hasNext(BufferedRowIterator.java:43)
> at
> org.apache.spark.sql.execution.WholeStageCodegenExec$$anonfun$8$$anon$1.hasNext(WholeStageCodegenExec.scala:370)
> at
> org.apache.spark.sql.execution.debug.package$DebugExec$$anonfun$3$$anon$1.hasNext(package.scala:146)
> at org.apache.spark.util.Utils$.getIteratorSize(Utils.scala:1763)
> at org.apache.spark.rdd.RDD$$anonfun$count$1.apply(RDD.scala:1134)
> at org.apache.spark.rdd.RDD$$anonfun$count$1.apply(RDD.scala:1134)
> at
> org.apache.spark.SparkContext$$anonfun$runJob$5.apply(SparkContext.scala:1899)
> at
> org.apache.spark.SparkContext$$anonfun$runJob$5.apply(SparkContext.scala:1899)
> at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:70)
> at org.apache.spark.scheduler.Task.run(Task.scala:86)
> at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:274)
> at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> at java.lang.Thread.run(Thread.java:745)
> {code}
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