[SPARK-20291][SQL] NaNvl(FloatType, NullType) should not be cast to NaNvl(DoubleType, DoubleType)

## What changes were proposed in this pull request?

`NaNvl(float value, null)` will be converted into `NaNvl(float value, Cast(null, DoubleType))` and finally `NaNvl(Cast(float value, DoubleType), Cast(null, DoubleType))`.

This will cause mismatching in the output type when the input type is float.

By adding extra rule in TypeCoercion can resolve this issue.

## How was this patch tested?

unite tests.

Please review http://spark.apache.org/contributing.html before opening a pull request.

Author: DB Tsai <dbt@netflix.com>

Closes #17606 from dbtsai/fixNaNvl.

1 files changed, 1 insertions, 2 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/DataFrameNaFunctions.scala b/sql/core/src/main/scala/org/apache/spark/sql/DataFrameNaFunctions.scala
index 93d565d9fe..052d85ad33 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/DataFrameNaFunctions.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/DataFrameNaFunctions.scala
@@ -408,8 +408,7 @@ final class DataFrameNaFunctions private[sql](df: DataFrame) {
     val quotedColName = "`" + col.name + "`"
     val colValue = col.dataType match {
       case DoubleType | FloatType =>
-        // nanvl only supports these types
-        nanvl(df.col(quotedColName), lit(null).cast(col.dataType))
+        nanvl(df.col(quotedColName), lit(null)) // nanvl only supports these types
       case _ => df.col(quotedColName)
     }
     coalesce(colValue, lit(replacement).cast(col.dataType)).as(col.name)