Scala Dataframe :如何使用两个Dataframe之间的条件向Dataframe添加列？

import org.apache.spark.sql.{DataFrame, SparkSession}
import org.apache.spark.sql.functions._

val spark = SparkSession.builder()
  .appName("DataFrame Example")
  .master("local")
  .getOrCreate()

val df1 = spark.createDataFrame(Seq(
  (1, "John"),
  (2, "Mike"),
  (3, "Lisa")
)).toDF("id", "name")

val df2 = spark.createDataFrame(Seq(
  (1, "USA"),
  (2, "Canada"),
  (3, "UK")
)).toDF("id", "country")

val joinedDf = df1.join(df2, Seq("id"), "inner")
  .withColumn("full_name", concat(col("name"), lit(" from "), col("country")))

joinedDf.show()

+---+----+-------+------------------+
| id|name|country|        full_name|
+---+----+-------+------------------+
|  1|John|    USA|John from USA     |
|  2|Mike| Canada|Mike from Canada  |
|  3|Lisa|     UK|Lisa from UK      |
+---+----+-------+------------------+