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

…aNvl(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 apache#17606 from dbtsai/fixNaNvl.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala

@@ -571,6 +571,7 @@ object TypeCoercion {
         NaNvl(l, Cast(r, DoubleType))
       case NaNvl(l, r) if l.dataType == FloatType && r.dataType == DoubleType =>
         NaNvl(Cast(l, DoubleType), r)
+      case NaNvl(l, r) if r.dataType == NullType => NaNvl(l, Cast(r, l.dataType))
     }
   }
 

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercionSuite.scala

@@ -656,14 +656,20 @@ class TypeCoercionSuite extends PlanTest {
 
   test("nanvl casts") {
     ruleTest(TypeCoercion.FunctionArgumentConversion,
-      NaNvl(Literal.create(1.0, FloatType), Literal.create(1.0, DoubleType)),
-      NaNvl(Cast(Literal.create(1.0, FloatType), DoubleType), Literal.create(1.0, DoubleType)))
+      NaNvl(Literal.create(1.0f, FloatType), Literal.create(1.0, DoubleType)),
+      NaNvl(Cast(Literal.create(1.0f, FloatType), DoubleType), Literal.create(1.0, DoubleType)))
     ruleTest(TypeCoercion.FunctionArgumentConversion,
-      NaNvl(Literal.create(1.0, DoubleType), Literal.create(1.0, FloatType)),
-      NaNvl(Literal.create(1.0, DoubleType), Cast(Literal.create(1.0, FloatType), DoubleType)))
+      NaNvl(Literal.create(1.0, DoubleType), Literal.create(1.0f, FloatType)),
+      NaNvl(Literal.create(1.0, DoubleType), Cast(Literal.create(1.0f, FloatType), DoubleType)))
     ruleTest(TypeCoercion.FunctionArgumentConversion,
       NaNvl(Literal.create(1.0, DoubleType), Literal.create(1.0, DoubleType)),
       NaNvl(Literal.create(1.0, DoubleType), Literal.create(1.0, DoubleType)))
+    ruleTest(TypeCoercion.FunctionArgumentConversion,
+      NaNvl(Literal.create(1.0f, FloatType), Literal.create(null, NullType)),
+      NaNvl(Literal.create(1.0f, FloatType), Cast(Literal.create(null, NullType), FloatType)))
+    ruleTest(TypeCoercion.FunctionArgumentConversion,
+      NaNvl(Literal.create(1.0, DoubleType), Literal.create(null, NullType)),
+      NaNvl(Literal.create(1.0, DoubleType), Cast(Literal.create(null, NullType), DoubleType)))
   }
 
   test("type coercion for If") {

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)