[
https://issues.apache.org/jira/browse/SPARK-19615?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15870513#comment-15870513
]
Nick Dimiduk commented on SPARK-19615:
--------------------------------------
IMHO, a union operation should be as generous as possible. This facilitates
common ETL and data cleansing operations where the sources are sparse-schema
structures (JSON, HBase, Elastic Search, &c). A couple examples of what I mean.
Given dataframes of type
{noformat}
root
|-- a: string (nullable = false)
|-- b: string (nullable = true)
{noformat}
and
{noformat}
root
|-- a: string (nullable = false)
|-- c: string (nullable = true)
{noformat}
I would expect the union operation to infer the nullable columns from both
sides to produce a dataframe of type
{noformat}
root
|-- a: string (nullable = false)
|-- b: string (nullable = true)
|-- c: string (nullable = true)
{noformat}
This should work on an arbitrarily deep nesting of structs, so
{noformat}
root
|-- a: string (nullable = false)
|-- b: struct (nullable = false)
| |-- b1: string (nullable = true)
| |-- b2: string (nullable = true)
{noformat}
unioned with
{noformat}
root
|-- a: string (nullable = false)
|-- b: struct (nullable = false)
| |-- b3: string (nullable = true)
| |-- b4: string (nullable = true)
{noformat}
would result in
{noformat}
root
|-- a: string (nullable = false)
|-- b: struct (nullable = false)
| |-- b1: string (nullable = true)
| |-- b2: string (nullable = true)
| |-- b3: string (nullable = true)
| |-- b4: string (nullable = true)
{noformat}
> Provide Dataset union convenience for divergent schema
> ------------------------------------------------------
>
> Key: SPARK-19615
> URL: https://issues.apache.org/jira/browse/SPARK-19615
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.1.0
> Reporter: Nick Dimiduk
> Priority: Minor
>
> Creating a union DataFrame over two sources that have different schema
> definitions is surprisingly complex. Provide a version of the union method
> that will create a infer a target schema as the result of merging the
> sources. Automatically add extend either side with {{null}} columns for any
> missing columns that are nullable.
--
This message was sent by Atlassian JIRA
(v6.3.15#6346)
---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscr...@spark.apache.org
For additional commands, e-mail: issues-h...@spark.apache.org
