[SPARK-31594][SQL] Do not display the seed of rand/randn with no argument in output schema

### What changes were proposed in this pull request?

This PR intends to update `sql` in `Rand`/`Randn` with no argument to make a column name deterministic.

Before this PR (a column name changes run-by-run):
```
scala> sql("select rand()").show()
+-------------------------+
|rand(7986133828002692830)|
+-------------------------+
|       0.9524061403696937|
+-------------------------+
```
After this PR (a column name fixed):
```
scala> sql("select rand()").show()
+------------------+
|            rand()|
+------------------+
|0.7137935639522275|
+------------------+

// If a seed given, it is still shown in a column name
// (the same with the current behaviour)
scala> sql("select rand(1)").show()
+------------------+
|           rand(1)|
+------------------+
|0.6363787615254752|
+------------------+

// We can still check a seed in explain output:
scala> sql("select rand()").explain()
== Physical Plan ==
*(1) Project [rand(-2282124938778456838) AS rand()#0]
+- *(1) Scan OneRowRelation[]
```

Note: This fix comes from #28194; the ongoing PR tests the output schema of expressions, so their schemas must be deterministic for the tests.

### Why are the changes needed?

To make output schema deterministic.

### Does this PR introduce any user-facing change?

No.

### How was this patch tested?

Added unit tests.

Closes #28392 from maropu/SPARK-31594.

Authored-by: Takeshi Yamamuro <yamamuro@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: maropu

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

@@ -83,9 +83,12 @@ trait ExpressionWithRandomSeed {
   """,
   since = "1.5.0")
 // scalastyle:on line.size.limit
-case class Rand(child: Expression) extends RDG with ExpressionWithRandomSeed {
+case class Rand(child: Expression, hideSeed: Boolean = false)
+  extends RDG with ExpressionWithRandomSeed {
 
-  def this() = this(Literal(Utils.random.nextLong(), LongType))
+  def this() = this(Literal(Utils.random.nextLong(), LongType), true)
+
+  def this(child: Expression) = this(child, false)
 
   override def withNewSeed(seed: Long): Rand = Rand(Literal(seed, LongType))
 
@@ -101,7 +104,12 @@ case class Rand(child: Expression) extends RDG with ExpressionWithRandomSeed {
       isNull = FalseLiteral)
   }
 
-  override def freshCopy(): Rand = Rand(child)
+  override def freshCopy(): Rand = Rand(child, hideSeed)
+
+  override def flatArguments: Iterator[Any] = Iterator(child)
+  override def sql: String = {
+    s"rand(${if (hideSeed) "" else child.sql})"
+  }
 }
 
 object Rand {
@@ -126,9 +134,12 @@ object Rand {
   """,
   since = "1.5.0")
 // scalastyle:on line.size.limit
-case class Randn(child: Expression) extends RDG with ExpressionWithRandomSeed {
+case class Randn(child: Expression, hideSeed: Boolean = false)
+  extends RDG with ExpressionWithRandomSeed {
 
-  def this() = this(Literal(Utils.random.nextLong(), LongType))
+  def this() = this(Literal(Utils.random.nextLong(), LongType), true)
+
+  def this(child: Expression) = this(child, false)
 
   override def withNewSeed(seed: Long): Randn = Randn(Literal(seed, LongType))
 
@@ -144,7 +155,12 @@ case class Randn(child: Expression) extends RDG with ExpressionWithRandomSeed {
       isNull = FalseLiteral)
   }
 
-  override def freshCopy(): Randn = Randn(child)
+  override def freshCopy(): Randn = Randn(child, hideSeed)
+
+  override def flatArguments: Iterator[Any] = Iterator(child)
+  override def sql: String = {
+    s"randn(${if (hideSeed) "" else child.sql})"
+  }
 }
 
 object Randn {

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

@@ -34,4 +34,11 @@ class RandomSuite extends SparkFunSuite with ExpressionEvalHelper {
     checkEvaluation(Rand(5419823303878592871L), 0.7145363364564755)
     checkEvaluation(Randn(5419823303878592871L), 0.7816815274533012)
   }
+
+  test("SPARK-31594: Do not display the seed of rand/randn with no argument in output schema") {
+    assert(Rand(Literal(1L), true).sql === "rand()")
+    assert(Randn(Literal(1L), true).sql === "randn()")
+    assert(Rand(Literal(1L), false).sql === "rand(1L)")
+    assert(Randn(Literal(1L), false).sql === "randn(1L)")
+  }
 }

sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala

@@ -3425,6 +3425,29 @@ class SQLQuerySuite extends QueryTest with SharedSparkSession with AdaptiveSpark
       assert(SQLConf.get.getConf(SQLConf.CODEGEN_FALLBACK) === true)
     }
   }
+
+  test("SPARK-31594: Do not display the seed of rand/randn with no argument in output schema") {
+    def checkIfSeedExistsInExplain(df: DataFrame): Unit = {
+      val output = new java.io.ByteArrayOutputStream()
+      Console.withOut(output) {
+        df.explain()
+      }
+      val projectExplainOutput = output.toString.split("\n").find(_.contains("Project")).get
+      assert(projectExplainOutput.matches(""".*randn?\(-?[0-9]+\).*"""))
+    }
+    val df1 = sql("SELECT rand()")
+    assert(df1.schema.head.name === "rand()")
+    checkIfSeedExistsInExplain(df1)
+    val df2 = sql("SELECT rand(1L)")
+    assert(df2.schema.head.name === "rand(1)")
+    checkIfSeedExistsInExplain(df2)
+    val df3 = sql("SELECT randn()")
+    assert(df3.schema.head.name === "randn()")
+    checkIfSeedExistsInExplain(df1)
+    val df4 = sql("SELECT randn(1L)")
+    assert(df4.schema.head.name === "randn(1)")
+    checkIfSeedExistsInExplain(df2)
+  }
 }
 
 case class Foo(bar: Option[String])