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From "Hyukjin Kwon (Jira)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-31657) CSV Writer writes no header for empty DataFrames
Date Sun, 10 May 2020 06:17:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-31657?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17103670#comment-17103670
] 

Hyukjin Kwon commented on SPARK-31657:
--------------------------------------

That's already fixed in the master:

{code]
>>> df1 = spark.sql("SELECT 1 as a")
>>> df1.limit(1).write.mode("OVERWRITE").option("Header", True).csv("data/test/csv")
>>> spark.read.option("Header", True).csv("data/test/csv").show()
+---+
|  a|
+---+
|  1|
+---+

>>> df1.limit(0).write.mode("OVERWRITE").option("Header", True).csv("data/test/csv")
>>> spark.read.option("Header", True).csv("data/test/csv").show()
+---+
|  a|
+---+
+---+
{code}

at SPARK-26208

> CSV Writer writes no header for empty DataFrames
> ------------------------------------------------
>
>                 Key: SPARK-31657
>                 URL: https://issues.apache.org/jira/browse/SPARK-31657
>             Project: Spark
>          Issue Type: Bug
>          Components: Input/Output
>    Affects Versions: 2.4.1
>         Environment: Local pyspark 2.41
>            Reporter: Furcy Pin
>            Priority: Minor
>
> When writing a DataFrame as csv with the Header option set to true,
> the header is not written when the DataFrame is empty.
> This creates failures for processes that read the csv back.
> Example (please notice the limit(0) in the second example):
> ```
>  
> {code:java}
> Welcome to
>  ____ __
>  / __/__ ___ _____/ /__
>  _\ \/ _ \/ _ `/ __/ '_/
>  /__ / .__/\_,_/_/ /_/\_\ version 2.4.1
>  /_/
> Using Python version 2.7.17 (default, Nov 7 2019 10:07:09)
> SparkSession available as 'spark'.
> >>> df1 = spark.sql("SELECT 1 as a")
> >>> df1.limit(1).write.mode("OVERWRITE").option("Header", True).csv("data/test/csv")
> >>> spark.read.option("Header", True).csv("data/test/csv").show()
> +---+
> | a|
> +---+
> | 1|
> +---+
> >>> 
> >>> df1.limit(0).write.mode("OVERWRITE").option("Header", True).csv("data/test/csv")
> >>> spark.read.option("Header", True).csv("data/test/csv").show()
> ++
> ||
> ++
> ++
> {code}
>  
> Expected behavior:
> {code:java}
> >>> df1.limit(0).write.mode("OVERWRITE").option("Header", True).csv("data/test/csv")
> >>> spark.read.option("Header", True).csv("data/test/csv").show()
> +---+
> | a|
> +---+
> +---+{code}



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