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大数据进阶之路——Spark SQL 之 DataFrame&&Dataset

孙中明发表于 2022/01/23 00:05:21 2022/01/23

1.6k+ 0 0

【摘要】文章目录 dataframe 和 rddAPI常用操作DataFrame和RDD案例DataSet DataFrame它不是Spark SQL提出的，而是早起在R、Pandas语言就...

文章目录

A Dataset is a distributed collection of data：分布式的数据集
A DataFrame is a Dataset organized into named columns.
以列（列名、列的类型、列值）的形式构成的分布式数据集，按照列赋予不同的名称

dataframe 和 rdd

DataFrame是一种以RDD为基础的分布式数据集，类似于传统数据库中的二维表格。DataFrame引入了schema。

RDD	DataFrame
java/scala ==> jvm	java/scala/python ==> Logic Plan
python ==> python runtime
Spark框架本身不了解Person类的内部结构	Spark SQL可以清楚地知道该数据集中包含哪些列，每列的名称和类型各是什么

API常用操作

package org.example

import org.apache.spark.sql.SparkSession

object DataFrameApp {

  def main(args: Array[String]) {

    val spark = SparkSession.builder().appName("DataFrameApp").master("local[2]").getOrCreate()

    // 将json文件加载成一个dataframe
    val peopleDF = spark.read.format("json").load("people.json")

    // 输出dataframe对应的schema信息
    peopleDF.printSchema()

    // 输出数据集的前20条记录
    peopleDF.show()

    //查询某列所有的数据： select name from table
    peopleDF.select("name").show()

    // 查询某几列所有的数据，并对列进行计算： select name, age+10 as age2 from table
    peopleDF.select(peopleDF.col("name"), (peopleDF.col("age") + 10).as("age2")).show()

    //根据某一列的值进行过滤： select * from table where age>19
    peopleDF.filter(peopleDF.col("age") > 19).show()

    //根据某一列进行分组，然后再进行聚合操作： select age,count(1) from table group by age
    peopleDF.groupBy("age").count().show()

    spark.stop()
  }
}
  
 
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root
 |-- age: long (nullable = true)
 |-- name: string (nullable = true)
+----+-------+
| age|   name|
+----+-------+
|null|Michael|
|  30|   Andy|
|  19| Justin|
+----+-------+
+-------+
|   name|
+-------+
|Michael|
|   Andy|
| Justin|
+-------+

+-------+----+
|   name|age2|
+-------+----+
|Michael|null|
|   Andy|  40|
| Justin|  29|
+-------+----+
+---+----+
|age|name|
+---+----+
| 30|Andy|
+---+----+

+----+-----+
| age|count|
+----+-----+
|  19|    1|
|null|    1|
|  30|    1|
+----+-----+
  
 
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DataFrame和RDD

package org.example

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

object DataFrameRDDApp {
  def main(args: Array[String]) {

    val spark = SparkSession.builder().appName("DataFrameRDDApp").master("local[2]").getOrCreate()

    //inferReflection(spark)

    program(spark)

    spark.stop()

  }

  def program(spark: SparkSession): Unit = {
    // RDD ==> DataFrame
    val rdd = spark.sparkContext.textFile("infos.txt")

    val infoRDD = rdd.map(_.split(",")).map(line => Row(line(0).toInt, line(1), line(2).toInt))

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

    val infoDF = spark.createDataFrame(infoRDD, structType)
    infoDF.printSchema()
    infoDF.show()
    //通过df的api进行操作
    infoDF.filter(infoDF.col("age") > 70).show

    //通过sql的方式进行操作
    infoDF.createOrReplaceTempView("infos")
    spark.sql("select * from infos where age > 70").show()
  }

  def inferReflection(spark: SparkSession) {
    // RDD ==> DataFrame
    val rdd = spark.sparkContext.textFile("infos.txt")

    //注意：需要导入隐式转换
    import spark.implicits._
    val infoDF = rdd.map(_.split(",")).map(line => Info(line(0).toInt, line(1), line(2).toInt)).toDF()

    infoDF.show()

    infoDF.filter(infoDF.col("age") > 70).show

    infoDF.createOrReplaceTempView("infos")
    spark.sql("select * from infos where age > 70").show()
  }

  case class Info(id: Int, name: String, age: Int)

}
  
 
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root
 |-- id: integer (nullable = true)
 |-- name: string (nullable = true)
 |-- age: integer (nullable = true)
+---+-----+---+
| id| name|age|
+---+-----+---+
|  1|hello| 66|
|  2|world| 89|
|  3|spark| 88|
+---+-----+---+

+---+-----+---+
| id| name|age|
+---+-----+---+
|  2|world| 89|
|  3|spark| 88|
+---+-----+---+
+---+-----+---+
| id| name|age|
+---+-----+---+
|  2|world| 89|
|  3|spark| 88|
+---+-----+---+
  
 
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案例

package org.example
import org.apache.spark.sql.SparkSession

/**
 * DataFrame中的操作操作
 */
object DataFrameProjectApp {

  def main(args: Array[String]) {
    val spark = SparkSession.builder().appName("DataFrameProjectApp").master("local[2]").getOrCreate()

    // RDD ==> DataFrame
    val rdd = spark.sparkContext.textFile("Student.data")

    //注意：需要导入隐式转换
    import spark.implicits._
    val studentDF = rdd.map(_.split("\\|")).map(line => Student(line(0).toInt, line(1), line(2), line(3))).toDF()

    //show默认只显示前20条
    studentDF.show
    studentDF.show(30)
    studentDF.show(30, false)

    studentDF.take(10)
    studentDF.first()
    studentDF.head(3)
    studentDF.select("email").show(30,false)
    studentDF.filter("name=''").show
    studentDF.filter("name='' OR name='NULL'").show
    //name以M开头的人
    studentDF.filter("SUBSTR(name,0,1)='M'").show

    studentDF.sort(studentDF("name")).show
    studentDF.sort(studentDF("name").desc).show

    studentDF.sort("name","id").show
    studentDF.sort(studentDF("name").asc, studentDF("id").desc).show

    studentDF.select(studentDF("name").as("student_name")).show
    val studentDF2 = rdd.map(_.split("\\|")).map(line => Student(line(0).toInt, line(1), line(2), line(3))).toDF()

    studentDF.join(studentDF2, studentDF.col("id") === studentDF2.col("id")).show

    spark.stop()
  }

  case class Student(id: Int, name: String, phone: String, email: String)

}
  
 
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+---+--------+--------------+--------------------+
| id|    name|         phone|               email|
+---+--------+--------------+--------------------+
|  1|   Burke|1-300-746-8446|ullamcorper.velit...|
|  2|   Kamal|1-668-571-5046|pede.Suspendisse@...|
|  3|    Olga|1-956-311-1686|Aenean.eget.metus...|
|  4|   Belle|1-246-894-6340|vitae.aliquet.nec...|
|  5|  Trevor|1-300-527-4967|dapibus.id@acturp...|
|  6|  Laurel|1-691-379-9921|adipiscing@consec...|
|  7|    Sara|1-608-140-1995|Donec.nibh@enimEt...|
|  8|  Kaseem|1-881-586-2689|cursus.et.magna@e...|
|  9|     Lev|1-916-367-5608|Vivamus.nisi@ipsu...|
| 10|    Maya|1-271-683-2698|accumsan.convalli...|
| 11|     Emi|1-467-270-1337|        est@nunc.com|
| 12|   Caleb|1-683-212-0896|Suspendisse@Quisq...|
| 13|Florence|1-603-575-2444|sit.amet.dapibus@...|
| 14|   Anika|1-856-828-7883|euismod@ligulaeli...|
| 15|   Tarik|1-398-171-2268|turpis@felisorci.com|
| 16|   Amena|1-878-250-3129|lorem.luctus.ut@s...|
| 17| Blossom|1-154-406-9596|Nunc.commodo.auct...|
| 18|     Guy|1-869-521-3230|senectus.et.netus...|
| 19| Malachi|1-608-637-2772|Proin.mi.Aliquam@...|
| 20|  Edward|1-711-710-6552|lectus@aliquetlib...|
+---+--------+--------------+--------------------+
only showing top 20 rows
| id|    name|         phone|               email|
+---+--------+--------------+--------------------+
|  1|   Burke|1-300-746-8446|ullamcorper.velit...|
|  2|   Kamal|1-668-571-5046|pede.Suspendisse@...|
|  3|    Olga|1-956-311-1686|Aenean.eget.metus...|
|  4|   Belle|1-246-894-6340|vitae.aliquet.nec...|
|  5|  Trevor|1-300-527-4967|dapibus.id@acturp...|
|  6|  Laurel|1-691-379-9921|adipiscing@consec...|
|  7|    Sara|1-608-140-1995|Donec.nibh@enimEt...|
|  8|  Kaseem|1-881-586-2689|cursus.et.magna@e...|
|  9|     Lev|1-916-367-5608|Vivamus.nisi@ipsu...|
| 10|    Maya|1-271-683-2698|accumsan.convalli...|
| 11|     Emi|1-467-270-1337|        est@nunc.com|
| 12|   Caleb|1-683-212-0896|Suspendisse@Quisq...|
| 13|Florence|1-603-575-2444|sit.amet.dapibus@...|
| 14|   Anika|1-856-828-7883|euismod@ligulaeli...|
| 15|   Tarik|1-398-171-2268|turpis@felisorci.com|
| 16|   Amena|1-878-250-3129|lorem.luctus.ut@s...|
| 17| Blossom|1-154-406-9596|Nunc.commodo.auct...|
| 18|     Guy|1-869-521-3230|senectus.et.netus...|
| 19| Malachi|1-608-637-2772|Proin.mi.Aliquam@...|
| 20|  Edward|1-711-710-6552|lectus@aliquetlib...|
| 21|        |1-711-710-6552|lectus@aliquetlib...|
| 22|        |1-711-710-6552|lectus@aliquetlib...|
| 23|    NULL|1-711-710-6552|lectus@aliquetlib...|
+---+--------+--------------+--------------------+
+---+--------+--------------+-----------------------------------------+
|id |name    |phone         |email                                    |
+---+--------+--------------+-----------------------------------------+
|1  |Burke   |1-300-746-8446|ullamcorper.velit.in@ametnullaDonec.co.uk|
|2  |Kamal   |1-668-571-5046|pede.Suspendisse@interdumenim.edu        |
|3  |Olga    |1-956-311-1686|Aenean.eget.metus@dictumcursusNunc.edu   |
|4  |Belle   |1-246-894-6340|vitae.aliquet.nec@neque.co.uk            |
|5  |Trevor  |1-300-527-4967|dapibus.id@acturpisegestas.net           |
|6  |Laurel  |1-691-379-9921|adipiscing@consectetueripsum.edu         |
|7  |Sara    |1-608-140-1995|Donec.nibh@enimEtiamimperdiet.edu        |
|8  |Kaseem  |1-881-586-2689|cursus.et.magna@euismod.org              |
|9  |Lev     |1-916-367-5608|Vivamus.nisi@ipsumdolor.com              |
|10 |Maya    |1-271-683-2698|accumsan.convallis@ornarelectusjusto.edu |
|11 |Emi     |1-467-270-1337|est@nunc.com                             |
|12 |Caleb   |1-683-212-0896|Suspendisse@Quisque.edu                  |
|13 |Florence|1-603-575-2444|sit.amet.dapibus@lacusAliquamrutrum.ca   |
|14 |Anika   |1-856-828-7883|euismod@ligulaelit.co.uk                 |
|15 |Tarik   |1-398-171-2268|turpis@felisorci.com                     |
|16 |Amena   |1-878-250-3129|lorem.luctus.ut@scelerisque.com          |
|17 |Blossom |1-154-406-9596|Nunc.commodo.auctor@eratSed.co.uk        |
|18 |Guy     |1-869-521-3230|senectus.et.netus@lectusrutrum.com       |
|19 |Malachi |1-608-637-2772|Proin.mi.Aliquam@estarcu.net             |
|20 |Edward  |1-711-710-6552|lectus@aliquetlibero.co.uk               |
|21 |        |1-711-710-6552|lectus@aliquetlibero.co.uk               |
|22 |        |1-711-710-6552|lectus@aliquetlibero.co.uk               |
|23 |NULL    |1-711-710-6552|lectus@aliquetlibero.co.uk               |
+---+--------+--------------+-----------------------------------------+
+-----------------------------------------+
|email                                    |
+-----------------------------------------+
|ullamcorper.velit.in@ametnullaDonec.co.uk|
|pede.Suspendisse@interdumenim.edu        |
|Aenean.eget.metus@dictumcursusNunc.edu   |
|vitae.aliquet.nec@neque.co.uk            |
|dapibus.id@acturpisegestas.net           |
|adipiscing@consectetueripsum.edu         |
|Donec.nibh@enimEtiamimperdiet.edu        |
|cursus.et.magna@euismod.org              |
|Vivamus.nisi@ipsumdolor.com              |
|accumsan.convallis@ornarelectusjusto.edu |
|est@nunc.com                             |
|Suspendisse@Quisque.edu                  |
|sit.amet.dapibus@lacusAliquamrutrum.ca   |
|euismod@ligulaelit.co.uk                 |
|turpis@felisorci.com                     |
|lorem.luctus.ut@scelerisque.com          |
|Nunc.commodo.auctor@eratSed.co.uk        |
|senectus.et.netus@lectusrutrum.com       |
|Proin.mi.Aliquam@estarcu.net             |
|lectus@aliquetlibero.co.uk               |
|lectus@aliquetlibero.co.uk               |
|lectus@aliquetlibero.co.uk               |
|lectus@aliquetlibero.co.uk               |
+-----------------------------------------+
+---+----+--------------+--------------------+
| id|name|         phone|               email|
+---+----+--------------+--------------------+
| 21|    |1-711-710-6552|lectus@aliquetlib...|
| 22|    |1-711-710-6552|lectus@aliquetlib...|
+---+----+--------------+--------------------+
+---+----+--------------+--------------------+
| id|name|         phone|               email|
+---+----+--------------+--------------------+
| 21|    |1-711-710-6552|lectus@aliquetlib...|
| 22|    |1-711-710-6552|lectus@aliquetlib...|
| 23|NULL|1-711-710-6552|lectus@aliquetlib...|
+---+----+--------------+--------------------+

+---+-------+--------------+--------------------+
| id|   name|         phone|               email|
+---+-------+--------------+--------------------+
| 10|   Maya|1-271-683-2698|accumsan.convalli...|
| 19|Malachi|1-608-637-2772|Proin.mi.Aliquam@...|
+---+-------+--------------+--------------------+
+---+--------+--------------+--------------------+
| id|    name|         phone|               email|
+---+--------+--------------+--------------------+
| 21|        |1-711-710-6552|lectus@aliquetlib...|
| 22|        |1-711-710-6552|lectus@aliquetlib...|
| 16|   Amena|1-878-250-3129|lorem.luctus.ut@s...|
| 14|   Anika|1-856-828-7883|euismod@ligulaeli...|
|  4|   Belle|1-246-894-6340|vitae.aliquet.nec...|
| 17| Blossom|1-154-406-9596|Nunc.commodo.auct...|
|  1|   Burke|1-300-746-8446|ullamcorper.velit...|
| 12|   Caleb|1-683-212-0896|Suspendisse@Quisq...|
| 20|  Edward|1-711-710-6552|lectus@aliquetlib...|
| 11|     Emi|1-467-270-1337|        est@nunc.com|
| 13|Florence|1-603-575-2444|sit.amet.dapibus@...|
| 18|     Guy|1-869-521-3230|senectus.et.netus...|
|  2|   Kamal|1-668-571-5046|pede.Suspendisse@...|
|  8|  Kaseem|1-881-586-2689|cursus.et.magna@e...|
|  6|  Laurel|1-691-379-9921|adipiscing@consec...|
|  9|     Lev|1-916-367-5608|Vivamus.nisi@ipsu...|
| 19| Malachi|1-608-637-2772|Proin.mi.Aliquam@...|
| 10|    Maya|1-271-683-2698|accumsan.convalli...|
| 23|    NULL|1-711-710-6552|lectus@aliquetlib...|
|  3|    Olga|1-956-311-1686|Aenean.eget.metus...|
+---+--------+--------------+--------------------+
+---+--------+--------------+--------------------+
| id|    name|         phone|               email|
+---+--------+--------------+--------------------+
|  5|  Trevor|1-300-527-4967|dapibus.id@acturp...|
| 15|   Tarik|1-398-171-2268|turpis@felisorci.com|
|  7|    Sara|1-608-140-1995|Donec.nibh@enimEt...|
|  3|    Olga|1-956-311-1686|Aenean.eget.metus...|
| 23|    NULL|1-711-710-6552|lectus@aliquetlib...|
| 10|    Maya|1-271-683-2698|accumsan.convalli...|
| 19| Malachi|1-608-637-2772|Proin.mi.Aliquam@...|
|  9|     Lev|1-916-367-5608|Vivamus.nisi@ipsu...|
|  6|  Laurel|1-691-379-9921|adipiscing@consec...|
|  8|  Kaseem|1-881-586-2689|cursus.et.magna@e...|
|  2|   Kamal|1-668-571-5046|pede.Suspendisse@...|
| 18|     Guy|1-869-521-3230|senectus.et.netus...|
| 13|Florence|1-603-575-2444|sit.amet.dapibus@...|
| 11|     Emi|1-467-270-1337|        est@nunc.com|
| 20|  Edward|1-711-710-6552|lectus@aliquetlib...|
| 12|   Caleb|1-683-212-0896|Suspendisse@Quisq...|
|  1|   Burke|1-300-746-8446|ullamcorper.velit...|
| 17| Blossom|1-154-406-9596|Nunc.commodo.auct...|
|  4|   Belle|1-246-894-6340|vitae.aliquet.nec...|
| 14|   Anika|1-856-828-7883|euismod@ligulaeli...|
+---+--------+--------------+--------------------+
+---+--------+--------------+--------------------+
| id|    name|         phone|               email|
+---+--------+--------------+--------------------+
| 21|        |1-711-710-6552|lectus@aliquetlib...|
| 22|        |1-711-710-6552|lectus@aliquetlib...|
| 16|   Amena|1-878-250-3129|lorem.luctus.ut@s...|
| 14|   Anika|1-856-828-7883|euismod@ligulaeli...|
|  4|   Belle|1-246-894-6340|vitae.aliquet.nec...|
| 17| Blossom|1-154-406-9596|Nunc.commodo.auct...|
|  1|   Burke|1-300-746-8446|ullamcorper.velit...|
| 12|   Caleb|1-683-212-0896|Suspendisse@Quisq...|
| 20|  Edward|1-711-710-6552|lectus@aliquetlib...|
| 11|     Emi|1-467-270-1337|        est@nunc.com|
| 13|Florence|1-603-575-2444|sit.amet.dapibus@...|
| 18|     Guy|1-869-521-3230|senectus.et.netus...|
|  2|   Kamal|1-668-571-5046|pede.Suspendisse@...|
|  8|  Kaseem|1-881-586-2689|cursus.et.magna@e...|
|  6|  Laurel|1-691-379-9921|adipiscing@consec...|
|  9|     Lev|1-916-367-5608|Vivamus.nisi@ipsu...|
| 19| Malachi|1-608-637-2772|Proin.mi.Aliquam@...|
| 10|    Maya|1-271-683-2698|accumsan.convalli...|
| 23|    NULL|1-711-710-6552|lectus@aliquetlib...|
|  3|    Olga|1-956-311-1686|Aenean.eget.metus...|
+---+--------+--------------+--------------------+
+---+--------+--------------+--------------------+
| id|    name|         phone|               email|
+---+--------+--------------+--------------------+
| 22|        |1-711-710-6552|lectus@aliquetlib...|
| 21|        |1-711-710-6552|lectus@aliquetlib...|
| 16|   Amena|1-878-250-3129|lorem.luctus.ut@s...|
| 14|   Anika|1-856-828-7883|euismod@ligulaeli...|
|  4|   Belle|1-246-894-6340|vitae.aliquet.nec...|
| 17| Blossom|1-154-406-9596|Nunc.commodo.auct...|
|  1|   Burke|1-300-746-8446|ullamcorper.velit...|
| 12|   Caleb|1-683-212-0896|Suspendisse@Quisq...|
| 20|  Edward|1-711-710-6552|lectus@aliquetlib...|
| 11|     Emi|1-467-270-1337|        est@nunc.com|
| 13|Florence|1-603-575-2444|sit.amet.dapibus@...|
| 18|     Guy|1-869-521-3230|senectus.et.netus...|
|  2|   Kamal|1-668-571-5046|pede.Suspendisse@...|
|  8|  Kaseem|1-881-586-2689|cursus.et.magna@e...|
|  6|  Laurel|1-691-379-9921|adipiscing@consec...|
|  9|     Lev|1-916-367-5608|Vivamus.nisi@ipsu...|
| 19| Malachi|1-608-637-2772|Proin.mi.Aliquam@...|
| 10|    Maya|1-271-683-2698|accumsan.convalli...|
| 23|    NULL|1-711-710-6552|lectus@aliquetlib...|
|  3|    Olga|1-956-311-1686|Aenean.eget.metus...|
+---+--------+--------------+--------------------+

+------------+
|student_name|
+------------+
|       Burke|
|       Kamal|
|        Olga|
|       Belle|
|      Trevor|
|      Laurel|
|        Sara|
|      Kaseem|
|         Lev|
|        Maya|
|         Emi|
|       Caleb|
|    Florence|
|       Anika|
|       Tarik|
|       Amena|
|     Blossom|
|         Guy|
|     Malachi|
|      Edward|
+------------+
+---+--------+--------------+--------------------+---+--------+--------------+--------------------+
| id|    name|         phone|               email| id|    name|         phone|               email|
+---+--------+--------------+--------------------+---+--------+--------------+--------------------+
| 12|   Caleb|1-683-212-0896|Suspendisse@Quisq...| 12|   Caleb|1-683-212-0896|Suspendisse@Quisq...|
| 22|        |1-711-710-6552|lectus@aliquetlib...| 22|        |1-711-710-6552|lectus@aliquetlib...|
|  1|   Burke|1-300-746-8446|ullamcorper.velit...|  1|   Burke|1-300-746-8446|ullamcorper.velit...|
| 13|Florence|1-603-575-2444|sit.amet.dapibus@...| 13|Florence|1-603-575-2444|sit.amet.dapibus@...|
|  6|  Laurel|1-691-379-9921|adipiscing@consec...|  6|  Laurel|1-691-379-9921|adipiscing@consec...|
| 16|   Amena|1-878-250-3129|lorem.luctus.ut@s...| 16|   Amena|1-878-250-3129|lorem.luctus.ut@s...|
|  3|    Olga|1-956-311-1686|Aenean.eget.metus...|  3|    Olga|1-956-311-1686|Aenean.eget.metus...|
| 20|  Edward|1-711-710-6552|lectus@aliquetlib...| 20|  Edward|1-711-710-6552|lectus@aliquetlib...|
|  5|  Trevor|1-300-527-4967|dapibus.id@acturp...|  5|  Trevor|1-300-527-4967|dapibus.id@acturp...|
| 19| Malachi|1-608-637-2772|Proin.mi.Aliquam@...| 19| Malachi|1-608-637-2772|Proin.mi.Aliquam@...|
| 15|   Tarik|1-398-171-2268|turpis@felisorci.com| 15|   Tarik|1-398-171-2268|turpis@felisorci.com|
|  9|     Lev|1-916-367-5608|Vivamus.nisi@ipsu...|  9|     Lev|1-916-367-5608|Vivamus.nisi@ipsu...|
| 17| Blossom|1-154-406-9596|Nunc.commodo.auct...| 17| Blossom|1-154-406-9596|Nunc.commodo.auct...|
|  4|   Belle|1-246-894-6340|vitae.aliquet.nec...|  4|   Belle|1-246-894-6340|vitae.aliquet.nec...|
|  8|  Kaseem|1-881-586-2689|cursus.et.magna@e...|  8|  Kaseem|1-881-586-2689|cursus.et.magna@e...|
| 23|    NULL|1-711-710-6552|lectus@aliquetlib...| 23|    NULL|1-711-710-6552|lectus@aliquetlib...|
|  7|    Sara|1-608-140-1995|Donec.nibh@enimEt...|  7|    Sara|1-608-140-1995|Donec.nibh@enimEt...|
| 10|    Maya|1-271-683-2698|accumsan.convalli...| 10|    Maya|1-271-683-2698|accumsan.convalli...|
| 21|        |1-711-710-6552|lectus@aliquetlib...| 21|        |1-711-710-6552|lectus@aliquetlib...|
| 11|     Emi|1-467-270-1337|        est@nunc.com| 11|     Emi|1-467-270-1337|        est@nunc.com|
+---+--------+--------------+--------------------+---+--------+--------------+--------------------+
only showing top 20 rows
  
 
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DataSet

DataFrame = Dataset[Row]
Dataset：强类型 typed case class
DataFrame：弱类型 Row

SQL: seletc name from person; compile ok, result no
DF:
- df.select(“name”) compile no
- df.select(“nname”) compile ok
DS:ds.map(line => line.itemid) compile no

文章来源: hiszm.blog.csdn.net，作者：孙中明，版权归原作者所有，如需转载，请联系作者。

原文链接：hiszm.blog.csdn.net/article/details/120570484

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