Daniel Darabos created SPARK-25146:
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Summary: avg() returns null on some decimals
Key: SPARK-25146
URL: https://issues.apache.org/jira/browse/SPARK-25146
Project: Spark
Issue Type: Bug
Components: SQL
Affects Versions: 2.3.1, 2.3.0
Reporter: Daniel Darabos
We compute some 0-10 numbers in a pipeline using Spark SQL. Then we average
them. The average in some cases comes out to {{null}} to our surprise (and
disappointment).
After a bit of digging it looks like these numbers have ended up with the
{{decimal(37,30)}} type. I've got a Spark Shell (2.3.0 and 2.3.1) repro with
this type:
{{scala> (1 to 10000).map(_*0.001).toDF.createOrReplaceTempView("x")}}
{{scala> spark.sql("select cast(value as decimal(37, 30)) as v from
x").createOrReplaceTempView("x")}}
{{scala> spark.sql("select avg(v) from x").show}}
{{+------+}}
{{|avg(v)|}}
{{+------+}}
{{| null|}}
{{+------+}}
For up to 4471 numbers it is able to calculate the average. For 4472 or more
numbers it's {{null}}.
Now I'll just change these numbers to {{double}}. But we got the types entirely
automatically. We never asked for {{decimal}}. If this is the default type,
it's important to support averaging a handful of them. (Sorry for the
bitterness. I like {{double}} more. :))
Curiously, {{sum()}} works. And {{count()}} too. So it's quite the surprise
that {{avg()}} fails.
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