## What changes were proposed in this pull request?
In Average.scala, it has
```
override lazy val evaluateExpression = child.dataType match {
case DecimalType.Fixed(p, s) =>
// increase the precision and scale to prevent precision loss
val dt = DecimalType.bounded(p + 14, s + 4)
Cast(Cast(sum, dt) / Cast(count, dt), resultType)
case _ =>
Cast(sum, resultType) / Cast(count, resultType)
}
def setChild (newchild: Expression) = {
child = newchild
}
```
It is possible that Cast(count, dt), resultType) will make the precision of the decimal number bigger than 38, and this causes over flow. Since count is an integer and doesn't need a scale, I will cast it using DecimalType.bounded(38,0)
## How was this patch tested?
In DataFrameSuite, I will add a test case.
Please review http://spark.apache.org/contributing.html before opening a pull request.
Author: Huaxin Gao <huaxing@us.ibm.com>
Closes#19496 from huaxingao/spark-22271.
28f9f3f225