如何在Spark 2.3.0中执行self join？正确的语法是什么？

val joinedDF = df1.as("a").join(df2.as("b"), condition, "joinType")

import org.apache.spark.sql.SparkSession

val spark = SparkSession.builder()
  .appName("Self Join")
  .master("local")
  .getOrCreate()

val df1 = spark.createDataFrame(Seq(
  (1, "A"),
  (2, "B"),
  (3, "C")
)).toDF("id", "name")

val df2 = spark.createDataFrame(Seq(
  (1, "X"),
  (2, "Y"),
  (3, "Z")
)).toDF("id", "value")

val joinedDF = df1.as("a").join(df2.as("b"), $"a.id" === $"b.id", "inner")

joinedDF.show()