Prasanna Saraswathi Krishnan created SPARK-29432:
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Summary: nullable flag of new column changes when persisting a
pyspark dataframe
Key: SPARK-29432
URL: https://issues.apache.org/jira/browse/SPARK-29432
Project: Spark
Issue Type: Question
Components: SQL
Affects Versions: 2.4.0
Environment: Spark 2.4.0-cdh6.1.1 (Cloudera distribution)
Python 3.7.3
Reporter: Prasanna Saraswathi Krishnan
When I add a new column to a dataframe with {{withColumn}} function, by
default, the column is added with {{nullable=false}}.
But, when I save the dataframe, the flag changes to {{nullable=true}}. Is this
the expected behavior? why?
{{>>> l = [('Alice', 1)]}}
{{>>> df = spark.createDataFrame(l)}}
{{>>> df.printSchema()}}
{{root}}
{{ |-- _1: string (nullable = true)}}
{{ |-- _2: long (nullable = true)}}
{{>>> from pyspark.sql.functions import lit}}
{{>>> df = df.withColumn('newCol', lit('newVal'))}}
{{>>> df.printSchema()}}
{{root}}
{{ |-- _1: string (nullable = true)}}
{{ |-- _2: long (nullable = true)}}
{{ |-- newCol: string (nullable = false)}}
{{>>> df.write.saveAsTable('default.withcolTest', mode='overwrite')}}
{{>>> spark.sql("select * from default.withcolTest").printSchema()}}
{{root}}
{{ |-- _1: string (nullable = true)}}
{{ |-- _2: long (nullable = true)}}
{{ |-- newCol: string (nullable = true)}}
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