[jira] (SPARK-37575) Null values are saved as quoted empty Strings "" rather than nothing

["Guo Wei (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-37575 ]


    Guo Wei deleted comment on SPARK-37575:
    ---------------------------------

was (Author: wayne guo):
I also found that if emptyValueInRead set to "\"\"", reading csv data as show below:
{noformat}
name,brand,comment
tesla,,""{noformat}
The final result shows as follows:
||name||brand||comment||
|tesla|null|""|

But, the expected result should be:
||name||brand||comment||
|tesla|null| |

> Null values are saved as quoted empty Strings "" rather than nothing
> --------------------------------------------------------------------
>
>                 Key: SPARK-37575
>                 URL: https://issues.apache.org/jira/browse/SPARK-37575
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 2.4.0, 3.2.0
>            Reporter: Guo Wei
>            Priority: Major
>
> As mentioned in sql migration guide([https://spark.apache.org/docs/latest/sql-migration-guide.html#upgrading-from-spark-sql-23-to-24]),
> {noformat}
> Since Spark 2.4, empty strings are saved as quoted empty strings "". In version 2.3 and earlier, empty strings are equal to null values and do not reflect to any characters in saved CSV files. For example, the row of "a", null, "", 1 was written as a,,,1. Since Spark 2.4, the same row is saved as a,,"",1. To restore the previous behavior, set the CSV option emptyValue to empty (not quoted) string.{noformat}
>  
> But actually, both empty strings and null values are saved as quoted empty Strings "" rather than "" (for empty strings) and nothing(for null values)。
> code:
> {code:java}
> val data = List("spark", null, "").toDF("name")
> data.coalesce(1).write.csv("spark_csv_test")
> {code}
>  actual result:
> {noformat}
> line1: spark
> line2: ""
> line3: ""{noformat}
> expected result:
> {noformat}
> line1: spark
> line2: 
> line3: ""
> {noformat}



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