[SPARK-43124][SQL] Dataset.show projects CommandResults locally

sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala

@@ -272,7 +272,13 @@ class Dataset[T] private[sql](
   private[sql] def getRows(
       numRows: Int,
       truncate: Int): Seq[Seq[String]] = {
-    val newDf = toDF()
+    val newDf = logicalPlan match {
+      case c: CommandResult =>
+        // Convert to `LocalRelation` and let `ConvertToLocalRelation` do the casting locally to
+        // avoid triggering a job
+        Dataset.ofRows(sparkSession, LocalRelation(c.output, c.rows))
+      case _ => toDF()
+    }
     val castCols = newDf.logicalPlan.output.map { col =>
       // Since binary types in top-level schema fields have a specific format to print,
       // so we do not cast them to strings here.

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

@@ -2474,6 +2474,25 @@ class DatasetSuite extends QueryTest
     )
     assert(result == expected)
   }
+
+  test("SPARK-43124: Show does not trigger job execution on CommandResults") {
+    withSQLConf(SQLConf.OPTIMIZER_EXCLUDED_RULES.key -> "") {
+      withTable("t1") {
+        sql("create table t1(c int) using parquet")
+
+        @volatile var jobCounter = 0
+        val listener = new SparkListener {
+          override def onJobStart(jobStart: SparkListenerJobStart): Unit = {
+            jobCounter += 1
+          }
+        }
+        withListener(spark.sparkContext, listener) { _ =>
+          sql("show tables").show()
+        }
+        assert(jobCounter === 0)
+      }
+    }
+  }
 }
 
 class DatasetLargeResultCollectingSuite extends QueryTest