[SPARK-23794][SQL] Make UUID as stateful expression

## What changes were proposed in this pull request?

The UUID() expression is stateful and should implement the `Stateful` trait instead of the `Nondeterministic` trait.

## How was this patch tested?

Added test.

Author: Liang-Chi Hsieh <[email protected]>

Closes apache#20912 from viirya/SPARK-23794.

Author: viirya

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/misc.scala

@@ -123,7 +123,7 @@ case class CurrentDatabase() extends LeafExpression with Unevaluable {
        46707d92-02f4-4817-8116-a4c3b23e6266
   """)
 // scalastyle:on line.size.limit
-case class Uuid(randomSeed: Option[Long] = None) extends LeafExpression with Nondeterministic {
+case class Uuid(randomSeed: Option[Long] = None) extends LeafExpression with Stateful {
 
   def this() = this(None)
 
@@ -152,4 +152,6 @@ case class Uuid(randomSeed: Option[Long] = None) extends LeafExpression with Non
     ev.copy(code = s"final UTF8String ${ev.value} = $randomGen.getNextUUIDUTF8String();",
       isNull = "false")
   }
+
+  override def freshCopy(): Uuid = Uuid(randomSeed)
 }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MiscExpressionsSuite.scala

@@ -59,6 +59,12 @@ class MiscExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper {
       evaluateWithGeneratedMutableProjection(Uuid(seed2)))
     assert(evaluateWithUnsafeProjection(Uuid(seed1)) !==
       evaluateWithUnsafeProjection(Uuid(seed2)))
+
+    val uuid = Uuid(seed1)
+    assert(uuid.fastEquals(uuid))
+    assert(!uuid.fastEquals(Uuid(seed1)))
+    assert(!uuid.fastEquals(uuid.freshCopy()))
+    assert(!uuid.fastEquals(Uuid(seed2)))
   }
 
   test("PrintToStderr") {