如何使用if else条件合并2个Spark数据帧

import org.apache.spark.sql.SparkSession
import org.apache.spark.sql.functions._

val spark = SparkSession.builder()
  .appName("Merge DataFrames with if else condition")
  .getOrCreate()

val DataFrame1 = spark.createDataFrame(Seq(
  (1, "John", 25),
  (2, "Jane", 30),
  (3, "Mike", 35)
)).toDF("id", "name", "age")

val DataFrame2 = spark.createDataFrame(Seq(
  (1, "USA"),
  (2, "Canada"),
  (4, "Australia")
)).toDF("id", "country")

val mergedDataFrame = DataFrame1.join(DataFrame2, Seq("id"), "left_outer")
  .withColumn("country", when(col("country").isNull, lit("Unknown")).otherwise(col("country")))

mergedDataFrame.show()