Spark之开窗函数

一.简介

　　开窗函数row_number()是按照某个字段分组，然后取另外一个字段排序的前几个值的函数，相当于分组topN。如果SQL语句里面使用了开窗函数，那么这个SQL语句必须使用HiveContext执行。

二.代码实践【使用HiveContext】

package big.data.analyse.sparksql

import org.apache.log4j.{Level, Logger}
import org.apache.spark.sql.types.{IntegerType, StringType, StructField, StructType}
import org.apache.spark.sql.{Row, SparkSession}

/**
  * Created by zhen on 2019/7/6.
  */
object RowNumber {
  /**
    * 设置日志级别
    */
  Logger.getLogger("org").setLevel(Level.WARN)
  def main(args: Array[String]) {
    /**
      * 创建spark入口，支持Hive
      */
    val spark = SparkSession.builder().appName("RowNumber")
      .master("local[2]").enableHiveSupport().getOrCreate()

    /**
      * 创建测试数据
      */
    val array = Array("1,Hadoop,12","5,Spark,6","3,Solr,15","3,HBase,8","6,Hive,16","6,TensorFlow,26")

    val rdd = spark.sparkContext.parallelize(array).map{ row =>
      val Array(id, name, age) = row.split(",")
      Row(id, name, age.toInt)
    }

    val structType = new StructType(Array(
      StructField("id", StringType, true),
      StructField("name", StringType, true),
      StructField("age", IntegerType, true)
    ))

    /**
      * 转化为df
      */
    val df = spark.createDataFrame(rdd, structType)
    df.show()

    df.createOrReplaceTempView("technology")

    /**
      * 应用开窗函数row_number
      * 注意：开窗函数只能在hiveContext下使用
      */
    val result_1 = spark.sql("select id,name,age from (select id,name,age," +
      "row_number() over (partition by id order by age desc) top from technology) t where t.top <= 1")
    result_1.show()

    val result_2 = spark.sql("select id,name,age from (select id,name,age," +
      "row_number() over (partition by id order by age desc) top from technology) t where t.top <= 2")
    result_2.show()

    val result_3 = spark.sql("select id,name,age from (select id,name,age," +
      "row_number() over (partition by id order by age desc) top from technology) t where t.top <= 3")
    result_3.show()

    val result_4 = spark.sql("select id,name,age from (select id,name,age," +
      "row_number() over (partition by id order by age desc) top from technology) t where t.top > 3")
    result_4.show()
  }
}

三.结果【使用HiveContext】

　　1.初始数据

　　　　

　　2.top<=1时

　　　　

　　3.top<=2时

　　　　

　　4.top<=3时

　　　　

　　5.top>3时【分组中最大为3】

　　　　

四.代码实现【不使用HiveContext】　

package big.data.analyse.sparksql

import org.apache.log4j.{Level, Logger}
import org.apache.spark.sql.types.{IntegerType, StringType, StructField, StructType}
import org.apache.spark.sql.{Row, SparkSession}

/**
  * Created by zhen on 2019/7/6.
  */
object RowNumber {
  /**
    * 设置日志级别
    */
  Logger.getLogger("org").setLevel(Level.WARN)
  def main(args: Array[String]) {
    /**
      * 创建spark入口，不支持Hive
      */
    val spark = SparkSession.builder().appName("RowNumber")
      .master("local[2]").getOrCreate()

    /**
      * 创建测试数据
      */
    val array = Array("1,Hadoop,12","5,Spark,6","3,Solr,15","3,HBase,8","6,Hive,16","6,TensorFlow,26")

    val rdd = spark.sparkContext.parallelize(array).map{ row =>
      val Array(id, name, age) = row.split(",")
      Row(id, name, age.toInt)
    }

    val structType = new StructType(Array(
      StructField("id", StringType, true),
      StructField("name", StringType, true),
      StructField("age", IntegerType, true)
    ))

    /**
      * 转化为df
      */
    val df = spark.createDataFrame(rdd, structType)
    df.show()

    df.createOrReplaceTempView("technology")

    /**
      * 应用开窗函数row_number
      * 注意：开窗函数只能在hiveContext下使用
      */
    val result_1 = spark.sql("select id,name,age from (select id,name,age," +
      "row_number() over (partition by id order by age desc) top from technology) t where t.top <= 1")
    result_1.show()

    val result_2 = spark.sql("select id,name,age from (select id,name,age," +
      "row_number() over (partition by id order by age desc) top from technology) t where t.top <= 2")
    result_2.show()

    val result_3 = spark.sql("select id,name,age from (select id,name,age," +
      "row_number() over (partition by id order by age desc) top from technology) t where t.top <= 3")
    result_3.show()

    val result_4 = spark.sql("select id,name,age from (select id,name,age," +
      "row_number() over (partition by id order by age desc) top from technology) t where t.top > 3")
    result_4.show()
  }
}

五.结果【不使用HiveContext】