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https://issues.apache.org/jira/browse/SPARK-38099?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17487435#comment-17487435
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L. C. Hsieh commented on SPARK-38099:
-------------------------------------
As this is not a bug, I will close this ticket then.
> Query using an aggregation on a literal value with an empty underlying
> dataframe returns null
> ---------------------------------------------------------------------------------------------
>
> Key: SPARK-38099
> URL: https://issues.apache.org/jira/browse/SPARK-38099
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 3.2.0
> Environment: Windows 10, Spark 3.2.0, Java 11.
> Reporter: Laurens Versluis
> Priority: Major
>
> Running a query with an aggregation functions such as average on literal
> value input with an empty dataframe in the FROM clause causes Spark to return
> null.
> Minimal reproducible example using Spark 3.2.0 with Java 11:
>
> {code:java}
> sparkSession.emptyDataFrame().createOrReplaceTempView("empty");
> StructType someSchema = new StructType(new
> StructField[]{DataTypes.createStructField("a", DataTypes.StringType, false)});
> final Row aRow = Row.fromSeq(asScalaBuffer(List.of("a")));
> sparkSession.createDataFrame(List.of(aRow),
> someSchema).createOrReplaceTempView("non_empty");
> sparkSession.sql("SELECT avg(1)").show(); // standalone query works
> sparkSession.sql("SELECT avg(1) FROM empty").show(); // empty DF gives null
> sparkSession.sql("SELECT avg(1) FROM non_empty").show(); // It does work with
> any non-empty DF{code}
> Output is as follows:
> {noformat}
> +------+
> |avg(1)|
> +------+
> | 1.0|
> +------+
> +------+
> |avg(1)|
> +------+
> | null|
> +------+
> +------+
> |avg(1)|
> +------+
> | 1.0|
> +------+
> {noformat}
> I would expect that the second query also returns 1.0. It seems that any
> non-empty DataFrame returns 1.0.
>
> Out of curiosity: is this Spark Catalyst doing some empty DataFrame
> optimizations that affect the result?
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