（1）RDD之間的join

import org.apache.spark.sql.SparkSession

object joinDemo {

  //BroadcastHashJoin
  def main(args: Array[String]): Unit = {
    val sparkSession = SparkSession.builder().appName("joinDemo").master("local[*]").getOrCreate()

    import sparkSession.implicits._

    val lines =sparkSession.createDataset(Array("1,hanmeimei,China","2,tom,USA","3,Jerry,apan"))
    //資料整理
    val tupleDS = lines.map(line=>{
      val field=line.split(",")
      val id = field(0).toLong
      val name = field(1)
      val country = field(2)
      (id,name,country)
    })

    val df1=tupleDS.toDF("id","name","country")

    val countrys = sparkSession.createDataset(List("China,中國","USA,美國"))
    val tupleDS2 =countrys.map(line=>{
      val fields = line.split(",")
      val ename = fields(0)
      val cname = fields(1)
      (ename,cname)
    })
    val df2 = tupleDS2.toDF("ename","cname")
    //建立一個檢視
    df1.createTempView("t_user")
    df2.createTempView("t_countrys")
    //join操作
    val res = sparkSession.sql("select u.id,u.name,c.cname from t_user as u join t_countrys as c on country=ename")
     res.show()

    //檢視執行計劃
    res.explain()

    sparkSession.stop()
  }

}
 

（2）DataFrame之間的join

import org.apache.spark.sql.{DataFrame, SparkSession}
object joinDemo2 {
  def main(args: Array[String]): Unit = {
    val sparkSession = SparkSession.builder().appName("joinDemo").master("local[*]").getOrCreate()

    import sparkSession.implicits._
    //對錶的大小不限制，預設10M
    sparkSession.conf.set("spark.sql.autoBroadcastJoinThreshold",-1)
    sparkSession.conf.set("spark.sql.join.preferSortMergeJoin",true)

    val df1: DataFrame =Seq(
      (0,"tom"),
      (1,"jeryy"),
      (2,"kate")
    ).toDF("id","name")
    
    val df2=Seq(
      (0,18),
      (1,20),
      (3,30)
    ).toDF("aid","age")

    df2.repartition()
    val res = df1.join(df2,$"id"===$"aid")
    res.explain()
    res.show()
  }
}