[jira] [Resolved] (SPARK-40808) Infer schema for CSV files - wrong behavior using header + merge schema

["zzzzming95 (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-40808?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

zzzzming95 resolved SPARK-40808.
--------------------------------
    Resolution: Fixed

expected behavior

> Infer schema for CSV files - wrong behavior using header + merge schema
> -----------------------------------------------------------------------
>
>                 Key: SPARK-40808
>                 URL: https://issues.apache.org/jira/browse/SPARK-40808
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 3.2.2
>            Reporter: ohad
>            Priority: Major
>              Labels: CSVReader, csv, csvparser
>         Attachments: test_csv.py
>
>
> Hello. 
> I am writing unit-tests to some functionality in my application that reading data from CSV files using Spark.
> I am reading the data using:
> {code:java}
> header=True
> mergeSchema=True
> inferSchema=True{code}
> When I am reading this single file:
> {code:java}
> File1:
> "int_col","string_col","decimal_col","date_col"
> 1,"hello",1.43,2022-02-23
> 2,"world",5.534,2021-05-05
> 3,"my name",86.455,2011-08-15
> 4,"is ohad",6.234,2002-03-22{code}
> I am getting this schema:
> {code:java}
> int_col=int
> string_col=string
> decimal_col=double
> date_col=string{code}
> When I am duplicating this file, I am getting the same schema.
> The strange part is when I am adding new int column, it looks like spark is getting confused and think that the column that already identified as int are now string:
> {code:java}
> File1:
> "int_col","string_col","decimal_col","date_col"
> 1,"hello",1.43,2022-02-23
> 2,"world",5.534,2021-05-05
> 3,"my name",86.455,2011-08-15
> 4,"is ohad",6.234,2002-03-22
> File2:
> "int_col","string_col","decimal_col","date_col","int2_col"
> 1,"hello",1.43,2022-02-23,234
> 2,"world",5.534,2021-05-05,5
> 3,"my name",86.455,2011-08-15,32
> 4,"is ohad",6.234,2002-03-22,2
> {code}
> result:
> {code:java}
> int_col=string
> string_col=string
> decimal_col=string
> date_col=string
> int2_col=int{code}
> When I am reading only the second file, it looks fine:
> {code:java}
> File2:
> "int_col","string_col","decimal_col","date_col","int2_col"
> 1,"hello",1.43,2022-02-23,234
> 2,"world",5.534,2021-05-05,5
> 3,"my name",86.455,2011-08-15,32
> 4,"is ohad",6.234,2002-03-22,2{code}
> result:
> {code:java}
> int_col=int
> string_col=string
> decimal_col=double
> date_col=string
> int2_col=int{code}
> For conclusion, it looks like there is a bug mixing the two features: header recognition and merge schema.



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