Spark sql的join

第一种：

import org.apache.spark.sql.{DataFrame, Dataset, SparkSession}

import scala.reflect.io.Path
object joinTest {

  def main(args: Array[String]): Unit = {
    val spark: SparkSession = SparkSession.builder()
      .appName("joinTest")
      .master("local[*]")
      .getOrCreate()
    import spark.implicits._
    val lines: Dataset[String] = spark.createDataset(List("1,jige,china","2,AJ,Japan","3,杨玉环,Tang"))

    //整理数据
    val Person: Dataset[(Int, String, String)] = lines.map(line => {
      val word: Array[String] = line.split(",")
      val id: Int = word(0).toInt
      val name: String = word(1).toString
      val country: String = word(2).toString
      (id, name, country)
    })
    val df1: DataFrame = Person.toDF("id","name","country")
    println("----df1----")
    df1.show()

    val lines2: Dataset[String] = spark.createDataset(Array("china,中国","Japan,日本"))
    val nations: Dataset[(String, String)] = lines2.map(x => {
      val word: Array[String] = x.split(",")
      val ename: String = word(0).toString
      val cname: String = word(1).toString
      (ename, cname)
    })
    val df2: DataFrame = nations.toDF("ename","cname")
    println("----df2----")
    df2.show()

    /**
      * 第一种：创建视图
      */
    df1.createTempView("t1")
    df2.createTempView("t2")
    //join语句：查询字段 + 第一张表 关联（join）第二张表 + 条件（on）+ 两张表字段相同
    val r: DataFrame = spark.sql("SELECT id,name,cname,ename FROM t1 JOIN t2 ON country = ename")
    println("----关联结果----")
    r.show()

    /**
      * 第二种，用dataframeAPI
      */
    //join连接类型有很多：`inner`, `cross`, `outer`, `full`, `full_outer`, `left`, `left_outer`,
    //   *                 `right`, `right_outer`, `left_semi`, `left_anti`.
    //如果最后不加join类型，默认是"inner"类型，等价于val rj: DataFrame = df1.join(df2,$"country" === $"ename")
    val rj: DataFrame = df1.join(df2,$"country" === $"ename","inner")
    println("----innerJoin----")
    rj.show()
    //左连接和左外连接结果相同`left`, `left_outer`
    val left: DataFrame = df1.join(df2,$"country" === $"ename","left")
    println("----leftJoin----")
    left.show()
  }

}
import org.apache.spark.s