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https://issues.apache.org/jira/browse/SPARK-10588?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14744149#comment-14744149
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Reynold Xin commented on SPARK-10588:
-------------------------------------
I think a more proper fix is to write the schema out as a metadata file ...
> Saving a DataFrame containing only nulls to JSON doesn't work
> -------------------------------------------------------------
>
> Key: SPARK-10588
> URL: https://issues.apache.org/jira/browse/SPARK-10588
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.5.0
> Reporter: Cheng Lian
> Priority: Minor
>
> Snippets to reproduce this issue:
> {noformat}
> val path = "file:///tmp/spark/null"
> // A single row containing a single null double, saving to JSON, wrong
> sqlContext.
> range(1).selectExpr("CAST(NULL AS DOUBLE) AS c0").
> write.mode("overwrite").json(path)
> sqlContext.read.json(path).show()
> ++
> ||
> ++
> ||
> ++
> // Two rows each containing a single null double, saving to JSON, wrong
> sqlContext.
> range(2).selectExpr("CAST(NULL AS DOUBLE) AS c0").
> write.mode("overwrite").json(path)
> sqlContext.read.json(path).show()
> ++
> ||
> ++
> ||
> ||
> ++
> // A single row containing two null doubles, saving to JSON, wrong
> sqlContext.
> range(1).selectExpr("CAST(NULL AS DOUBLE) AS c0", "CAST(NULL AS DOUBLE) AS
> c1").
> write.mode("overwrite").json(path)
> sqlContext.read.json(path).show()
> ++
> ||
> ++
> ||
> ++
> // A single row containing a single null double, saving to Parquet, OK
> sqlContext.
> range(1).selectExpr("CAST(NULL AS DOUBLE) AS c0").
> write.mode("overwrite").parquet(path)
> sqlContext.read.parquet(path).show()
> +----+
> | d|
> +----+
> |null|
> +----+
> // Two rows, one containing a single null double, one containing non-null
> double, saving to JSON, OK
> sqlContext.
> range(2).selectExpr("IF(id % 2 = 0, CAST(NULL AS DOUBLE), id) AS c0").
> write.mode("overwrite").json(path)
> sqlContext.read.json(path).show()
> +----+
> | d|
> +----+
> |null|
> | 1.0|
> +----+
> {noformat}
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