spark2 sql编程样例：sql操作

时间:2022-05-05
本文章向大家介绍spark2 sql编程样例：sql操作，主要内容包括其使用实例、应用技巧、基本知识点总结和需要注意事项，具有一定的参考价值，需要的朋友可以参考一下。

问题导读 1.DataFrame中本文使用了row哪些方法？ 2.操作DataFrame row需要导入什么包？ 3.teenagersDF.map(teenager => "Name: " + teenager(0)).show()中teenager 是什么trait？ 前两篇文章 spark2 sql读取数据源编程学习样例1：程序入口、功能等知识详解 http://www.aboutyun.com/forum.php?mod=viewthread&tid=23484 spark2 sql读取数据源编程学习样例2：函数实现详解 http://www.aboutyun.com/forum.php?mod=viewthread&tid=23489 写了关于spark sql如何读取数据源，下面说下spark sql的各种操作。 如果你想一个spark sql程序，那么你会想，你到底该使用哪个包，如何嵌入sql语句，如何创建表，如何显示表内容，如何指定表显示字段。下面解决了我们这些问题。同样我们先附上代码： 代码

[Scala] 纯文本查看 复制代码

?

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.spark.examples.sql
 
import org.apache.spark.sql.Row
// $example on:init_session$
import org.apache.spark.sql.SparkSession
// $example off:init_session$
// $example on:programmatic_schema$
// $example on:data_types$
import org.apache.spark.sql.types._
// $example off:data_types$
// $example off:programmatic_schema$
 
object SparkSQLExample {
 
  // $example on:create_ds$
  case class Person(name: String, age: Long)
  // $example off:create_ds$
 
  def main(args: Array[String]) {
    // $example on:init_session$
    val spark = SparkSession
      .builder()
      .appName("Spark SQL basic example")
      .config("spark.some.config.option", "some-value")
      .getOrCreate()
 
    // For implicit conversions like converting RDDs to DataFrames
    import spark.implicits._
    // $example off:init_session$
 
    runBasicDataFrameExample(spark)
    runDatasetCreationExample(spark)
    runInferSchemaExample(spark)
    runProgrammaticSchemaExample(spark)
 
    spark.stop()
  }
  private def runBasicDataFrameExample(spark: SparkSession): Unit = {
    // $example on:create_df$
    val df = spark.read.json("examples/src/main/resources/people.json")
 
    // Displays the content of the DataFrame to stdout
    df.show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+
    // $example off:create_df$
 
    // $example on:untyped_ops$
    // This import is needed to use the $-notation
    import spark.implicits._
    // Print the schema in a tree format
    df.printSchema()
    // root
    // |-- age: long (nullable = true)
    // |-- name: string (nullable = true)
 
    // Select only the "name" column
    df.select("name").show()
    // +-------+
    // |   name|
    // +-------+
    // |Michael|
    // |   Andy|
    // | Justin|
    // +-------+
 
    // Select everybody, but increment the age by 1
    df.select($"name", $"age" + 1).show()
    // +-------+---------+
    // |   name|(age + 1)|
    // +-------+---------+
    // |Michael|     null|
    // |   Andy|       31|
    // | Justin|       20|
    // +-------+---------+
 
    // Select people older than 21
    df.filter($"age" > 21).show()
    // +---+----+
    // |age|name|
    // +---+----+
    // | 30|Andy|
    // +---+----+
 
    // Count people by age
    df.groupBy("age").count().show()
    // +----+-----+
    // | age|count|
    // +----+-----+
    // |  19|    1|
    // |null|    1|
    // |  30|    1|
    // +----+-----+
    // $example off:untyped_ops$
 
    // $example on:run_sql$
    // Register the DataFrame as a SQL temporary view
    df.createOrReplaceTempView("people")
 
    val sqlDF = spark.sql("SELECT * FROM people")
    sqlDF.show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+
    // $example off:run_sql$
 
    // $example on:global_temp_view$
    // Register the DataFrame as a global temporary view
    df.createGlobalTempView("people")
 
    // Global temporary view is tied to a system preserved database `global_temp`
    spark.sql("SELECT * FROM global_temp.people").show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+
 
    // Global temporary view is cross-session
    spark.newSession().sql("SELECT * FROM global_temp.people").show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+
    // $example off:global_temp_view$
  }
 
  private def runDatasetCreationExample(spark: SparkSession): Unit = {
    import spark.implicits._
    // $example on:create_ds$
    // Encoders are created for case classes
    val caseClassDS = Seq(Person("Andy", 32)).toDS()
    caseClassDS.show()
    // +----+---+
    // |name|age|
    // +----+---+
    // |Andy| 32|
    // +----+---+
 
    // Encoders for most common types are automatically provided by importing spark.implicits._
    val primitiveDS = Seq(1, 2, 3).toDS()
    primitiveDS.map(_ + 1).collect() // Returns: Array(2, 3, 4)
 
    // DataFrames can be converted to a Dataset by providing a class. Mapping will be done by name
    val path = "examples/src/main/resources/people.json"
    val peopleDS = spark.read.json(path).as[Person]
    peopleDS.show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+
    // $example off:create_ds$
  }
 
  private def runInferSchemaExample(spark: SparkSession): Unit = {
    // $example on:schema_inferring$
    // For implicit conversions from RDDs to DataFrames
    import spark.implicits._
 
    // Create an RDD of Person objects from a text file, convert it to a Dataframe
    val peopleDF = spark.sparkContext
      .textFile("examples/src/main/resources/people.txt")
      .map(_.split(","))
      .map(attributes => Person(attributes(0), attributes(1).trim.toInt))
      .toDF()
    // Register the DataFrame as a temporary view
    peopleDF.createOrReplaceTempView("people")
 
    // SQL statements can be run by using the sql methods provided by Spark
    val teenagersDF = spark.sql("SELECT name, age FROM people WHERE age BETWEEN 13 AND 19")
 
    // The columns of a row in the result can be accessed by field index
    teenagersDF.map(teenager => "Name: " + teenager(0)).show()
    // +------------+
    // |       value|
    // +------------+
    // |Name: Justin|
    // +------------+
 
    // or by field name
    teenagersDF.map(teenager => "Name: " + teenager.getAs[String]("name")).show()
    // +------------+
    // |       value|
    // +------------+
    // |Name: Justin|
    // +------------+
 
    // No pre-defined encoders for Dataset[Map[K,V]], define explicitly
    implicit val mapEncoder = org.apache.spark.sql.Encoders.kryo[Map[String, Any]]
    // Primitive types and case classes can be also defined as
    // implicit val stringIntMapEncoder: Encoder[Map[String, Any]] = ExpressionEncoder()
 
    // row.getValuesMap[T] retrieves multiple columns at once into a Map[String, T]
    teenagersDF.map(teenager => teenager.getValuesMap[Any](List("name", "age"))).collect()
    // Array(Map("name" -> "Justin", "age" -> 19))
    // $example off:schema_inferring$
  }
 
  private def runProgrammaticSchemaExample(spark: SparkSession): Unit = {
    import spark.implicits._
    // $example on:programmatic_schema$
    // Create an RDD
    val peopleRDD = spark.sparkContext.textFile("examples/src/main/resources/people.txt")
 
    // The schema is encoded in a string
    val schemaString = "name age"
 
    // Generate the schema based on the string of schema
    val fields = schemaString.split(" ")
      .map(fieldName => StructField(fieldName, StringType, nullable = true))
    val schema = StructType(fields)
 
    // Convert records of the RDD (people) to Rows
    val rowRDD = peopleRDD
      .map(_.split(","))
      .map(attributes => Row(attributes(0), attributes(1).trim))
 
    // Apply the schema to the RDD
    val peopleDF = spark.createDataFrame(rowRDD, schema)
 
    // Creates a temporary view using the DataFrame
    peopleDF.createOrReplaceTempView("people")
 
    // SQL can be run over a temporary view created using DataFrames
    val results = spark.sql("SELECT name FROM people")
 
    // The results of SQL queries are DataFrames and support all the normal RDD operations
    // The columns of a row in the result can be accessed by field index or by field name
    results.map(attributes => "Name: " + attributes(0)).show()
    // +-------------+
    // |        value|
    // +-------------+
    // |Name: Michael|
    // |   Name: Andy|
    // | Name: Justin|
    // +-------------+
    // $example off:programmatic_schema$
  }
}

接着我们阅读代码： 包名

[Scala] 纯文本查看 复制代码

?

package org.apache.spark.examples.sql

同样还是先有一个自定义的包名org.apache.spark.examples.sql 导入包

[Scala] 纯文本查看 复制代码

?

import org.apache.spark.sql.Row
// $example on:init_session$
import org.apache.spark.sql.SparkSession
// $example off:init_session$
// $example on:programmatic_schema$
// $example on:data_types$
import org.apache.spark.sql.types._
// $example off:data_types$
// $example off:programmatic_schema$

上面我们导入了三个包，其中import org.apache.spark.sql.Row，import org.apache.spark.sql.types._是我们在读取数据源没有用到的。

[Scala] 纯文本查看 复制代码

?

case class Person(name: String, age: Long)

这里是自定义了一个类，跟普通类稍微有一些区别。 详细参考： scala中case class是什么？http://www.aboutyun.com/forum.php?mod=viewthread&tid=23464 程序入口

[Scala] 纯文本查看 复制代码

?

def main(args: Array[String]) {
    // $example on:init_session$
    val spark = SparkSession
      .builder()
      .appName("Spark SQL basic example")
      .config("spark.some.config.option", "some-value")
      .getOrCreate()
 
    // For implicit conversions like converting RDDs to DataFrames
    import spark.implicits._
    // $example off:init_session$
 
    runBasicDataFrameExample(spark)
    runDatasetCreationExample(spark)
    runInferSchemaExample(spark)
    runProgrammaticSchemaExample(spark)
 
    spark.stop()
  }

上面跟spark读取数据源是一样的，不在重复，想了解可查看 spark2 sql读取数据源编程学习样例1：程序入口、功能等知识详解 http://www.aboutyun.com/forum.php?mod=viewthread&tid=23484 runBasicDataFrameExample函数

[Scala] 纯文本查看 复制代码

?

private def runBasicDataFrameExample(spark: SparkSession): Unit = {
    // $example on:create_df$
    val df = spark.read.json("examples/src/main/resources/people.json")
 
    // Displays the content of the DataFrame to stdout
    df.show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+
    // $example off:create_df$
 
    // $example on:untyped_ops$
    // This import is needed to use the $-notation
    import spark.implicits._
    // Print the schema in a tree format
    df.printSchema()
    // root
    // |-- age: long (nullable = true)
    // |-- name: string (nullable = true)
 
    // Select only the "name" column
    df.select("name").show()
    // +-------+
    // |   name|
    // +-------+
    // |Michael|
    // |   Andy|
    // | Justin|
    // +-------+
 
    // Select everybody, but increment the age by 1
    df.select($"name", $"age" + 1).show()
    // +-------+---------+
    // |   name|(age + 1)|
    // +-------+---------+
    // |Michael|     null|
    // |   Andy|       31|
    // | Justin|       20|
    // +-------+---------+
 
    // Select people older than 21
    df.filter($"age" > 21).show()
    // +---+----+
    // |age|name|
    // +---+----+
    // | 30|Andy|
    // +---+----+
 
    // Count people by age
    df.groupBy("age").count().show()
    // +----+-----+
    // | age|count|
    // +----+-----+
    // |  19|    1|
    // |null|    1|
    // |  30|    1|
    // +----+-----+
    // $example off:untyped_ops$
 
    // $example on:run_sql$
    // Register the DataFrame as a SQL temporary view
    df.createOrReplaceTempView("people")
 
    val sqlDF = spark.sql("SELECT * FROM people")
    sqlDF.show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+
    // $example off:run_sql$
 
    // $example on:global_temp_view$
    // Register the DataFrame as a global temporary view
    df.createGlobalTempView("people")
 
    // Global temporary view is tied to a system preserved database `global_temp`
    spark.sql("SELECT * FROM global_temp.people").show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+
 
    // Global temporary view is cross-session
    spark.newSession().sql("SELECT * FROM global_temp.people").show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+
    // $example off:global_temp_view$
  }

这里面其实也有重复的，也不全部介绍了。其中

[Scala] 纯文本查看 复制代码

?

df.select("name").show()

是一直显示自定字段name的列表，如下：

[Scala] 纯文本查看 复制代码

?

// +-------+
   // |   name|
   // +-------+
   // |Michael|
   // |   Andy|
   // | Justin|
   // +-------+

[Scala] 纯文本查看 复制代码

?

df.select($"name", $"age" + 1).show()

上面我们还可以对字段操作，将字段的age都加1，并显示，如下：

[Scala] 纯文本查看 复制代码

?

// +-------+---------+
   // |   name|(age + 1)|
   // +-------+---------+
   // |Michael|     null|
   // |   Andy|       31|
   // | Justin|       20|
   // +-------+---------+

从这里说明Scala已经变的跟传统数据库差不多了。

[Scala] 纯文本查看 复制代码

?

df.filter($"age" > 21).show()
   // +---+----+
   // |age|name|
   // +---+----+
   // | 30|Andy|
   // +---+----+

上面查询是年龄大于21岁的记录。

[Scala] 纯文本查看 复制代码

?

// Count people by age
   df.groupBy("age").count().show()
   // +----+-----+
   // | age|count|
   // +----+-----+
   // |  19|    1|
   // |null|    1|
   // |  30|    1|
   // +----+-----+

上面则是分组，并统计。

[Scala] 纯文本查看 复制代码

?

// Register the DataFrame as a SQL temporary view
   df.createOrReplaceTempView("people")
 
   val sqlDF = spark.sql("SELECT * FROM people")
   sqlDF.show()
   // +----+-------+
   // | age|   name|
   // +----+-------+
   // |null|Michael|
   // |  30|   Andy|
   // |  19| Justin|
   // +----+-------+

上面是注册一个sql临时视图，然后查询显示

[Scala] 纯文本查看 复制代码

?

// Register the DataFrame as a global temporary view
    df.createGlobalTempView("people")
 
    // Global temporary view is tied to a system preserved database `global_temp`
    spark.sql("SELECT * FROM global_temp.people").show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+

我们看到这里有些区别带有global 。一个是people视图，一个是global_temp.people视图。

[Scala] 纯文本查看 复制代码

?

spark.newSession().sql("SELECT * FROM global_temp.people").show()    // +----+-------+
  // | age|   name|
  // +----+-------+
  // |null|Michael|
  // |  30|   Andy|
  // |  19| Justin|
  // +----+-------+

Global 临时视图是cross-session，也就是可能是不止在一个SparkSession中显示。当然这个后面在验证下。大家感兴趣也可以测试下。 runDatasetCreationExample函数

[Scala] 纯文本查看 复制代码

?

private def runDatasetCreationExample(spark: SparkSession): Unit = {
    import spark.implicits._
    // $example on:create_ds$
    // Encoders are created for case classes
    val caseClassDS = Seq(Person("Andy", 32)).toDS()
    caseClassDS.show()
    // +----+---+
    // |name|age|
    // +----+---+
    // |Andy| 32|
    // +----+---+
 
    // Encoders for most common types are automatically provided by importing spark.implicits._
    val primitiveDS = Seq(1, 2, 3).toDS()
    primitiveDS.map(_ + 1).collect() // Returns: Array(2, 3, 4)
 
    // DataFrames can be converted to a Dataset by providing a class. Mapping will be done by name
    val path = "examples/src/main/resources/people.json"
    val peopleDS = spark.read.json(path).as[Person]
    peopleDS.show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+
    // $example off:create_ds$
  }

整体来说实现了由集合分别转换为DataFrame和dataset。

[Scala] 纯文本查看 复制代码

?

val caseClassDS = Seq(Person("Andy", 32)).toDS()

上面是person类转换为序列，然后序列转换为DataFrame。

[Scala] 纯文本查看 复制代码

?

val primitiveDS = Seq(1, 2, 3).toDS()
   primitiveDS.map(_ + 1).collect() // Returns: Array(2, 3, 4)

从上面可以看出集合可以转换为dataset，然后通过map映射分别都加1，然后通过collect函数显示。

[Scala] 纯文本查看 复制代码

?

val path = "examples/src/main/resources/people.json"
    val peopleDS = spark.read.json(path).as[Person]
    peopleDS.show()
    // +----+-------+
    // | age|   name|
    // +----+-------+
    // |null|Michael|
    // |  30|   Andy|
    // |  19| Justin|
    // +----+-------+

上面其实很有意思

[Scala] 纯文本查看 复制代码

?

spark.read.json(path)

这里其实为DataFrame，但是通过

[Scala] 纯文本查看 复制代码

?

as[Person]

转换为了dataset，person则为case类。 runInferSchemaExample函数

[Scala] 纯文本查看 复制代码

?

private def runInferSchemaExample(spark: SparkSession): Unit = {
    // $example on:schema_inferring$
    // For implicit conversions from RDDs to DataFrames
    import spark.implicits._
 
    // Create an RDD of Person objects from a text file, convert it to a Dataframe
    val peopleDF = spark.sparkContext
      .textFile("examples/src/main/resources/people.txt")
      .map(_.split(","))
      .map(attributes => Person(attributes(0), attributes(1).trim.toInt))
      .toDF()
    // Register the DataFrame as a temporary view
    peopleDF.createOrReplaceTempView("people")
 
    // SQL statements can be run by using the sql methods provided by Spark
    val teenagersDF = spark.sql("SELECT name, age FROM people WHERE age BETWEEN 13 AND 19")
 
    // The columns of a row in the result can be accessed by field index
    teenagersDF.map(teenager => "Name: " + teenager(0)).show()
    // +------------+
    // |       value|
    // +------------+
    // |Name: Justin|
    // +------------+
 
    // or by field name
    teenagersDF.map(teenager => "Name: " + teenager.getAs[String]("name")).show()
    // +------------+
    // |       value|
    // +------------+
    // |Name: Justin|
    // +------------+
 
    // No pre-defined encoders for Dataset[Map[K,V]], define explicitly
    implicit val mapEncoder = org.apache.spark.sql.Encoders.kryo[Map[String, Any]]
    // Primitive types and case classes can be also defined as
    // implicit val stringIntMapEncoder: Encoder[Map[String, Any]] = ExpressionEncoder()
 
    // row.getValuesMap[T] retrieves multiple columns at once into a Map[String, T]
    teenagersDF.map(teenager => teenager.getValuesMap[Any](List("name", "age"))).collect()
    // Array(Map("name" -> "Justin", "age" -> 19))
    // $example off:schema_inferring$
  }

上面分别是rdd转换为DataFrame，以及DataFrame行的操作

[Scala] 纯文本查看 复制代码

?

val peopleDF = spark.sparkContext
      .textFile("examples/src/main/resources/people.txt")
      .map(_.split(","))
      .map(attributes => Person(attributes(0), attributes(1).trim.toInt))
      .toDF()

上面代码便是读取people.txt为rdd，然后转换为DataFrame。这里面大部分也重复了。需要说明的

[Scala] 纯文本查看 复制代码

?

implicit val mapEncoder = org.apache.spark.sql.Encoders.kryo[Map[String, Any]]

上面是map的序列化类mapEncoder 。

[Scala] 纯文本查看 复制代码

?

teenagersDF.map(teenager => "Name: " + teenager.getAs[String]("name")).show()
// +------------+
// |       value|
// +------------+
// |Name: Justin|
// +------------+

这里面值得说的getAs方法，它是DataFrame的row的方法，返回的是name字段的值 官网解释如下

[Scala] 纯文本查看 复制代码

?

teenagersDF.map(teenager => teenager.getValuesMap[Any](List("name", "age"))).collect()

teenager.getValuesMap[Any](List("name", "age"))这里是row的一个方法getValuesMap，获取指定几列的值 官网解释如下：

关于DataFrame row的更多操作方法，可参考 http://spark.apache.org/docs/latest/api/scala/index.html#org.apache.spark.sql.Row runProgrammaticSchemaExample函数

[Scala] 纯文本查看 复制代码

?

private def runProgrammaticSchemaExample(spark: SparkSession): Unit = {
    import spark.implicits._
    // $example on:programmatic_schema$
    // Create an RDD
    val peopleRDD = spark.sparkContext.textFile("examples/src/main/resources/people.txt")
 
    // The schema is encoded in a string
    val schemaString = "name age"
 
    // Generate the schema based on the string of schema
    val fields = schemaString.split(" ")
      .map(fieldName => StructField(fieldName, StringType, nullable = true))
    val schema = StructType(fields)
 
    // Convert records of the RDD (people) to Rows
    val rowRDD = peopleRDD
      .map(_.split(","))
      .map(attributes => Row(attributes(0), attributes(1).trim))
 
    // Apply the schema to the RDD
    val peopleDF = spark.createDataFrame(rowRDD, schema)
 
    // Creates a temporary view using the DataFrame
    peopleDF.createOrReplaceTempView("people")
 
    // SQL can be run over a temporary view created using DataFrames
    val results = spark.sql("SELECT name FROM people")
 
    // The results of SQL queries are DataFrames and support all the normal RDD operations
    // The columns of a row in the result can be accessed by field index or by field name
    results.map(attributes => "Name: " + attributes(0)).show()
    // +-------------+
    // |        value|
    // +-------------+
    // |Name: Michael|
    // |   Name: Andy|
    // | Name: Justin|
    // +-------------+
    // $example off:programmatic_schema$
  }

这个函数主要实现了，将RDD转换DataFrame的过程。

[Scala] 纯文本查看 复制代码

?

// The schema is encoded in a string
    val schemaString = "name age"
 
    // Generate the schema based on the string of schema
    val fields = schemaString.split(" ")
      .map(fieldName => StructField(fieldName, StringType, nullable = true))
    val schema = StructType(fields)
 
    // Convert records of the RDD (people) to Rows
    val rowRDD = peopleRDD
      .map(_.split(","))
      .map(attributes => Row(attributes(0), attributes(1).trim))

上面分别是创建一个字符串schemaString ，然后对schemaString处理，通过StructField和StructType转换为schema ，rowRDD 则是由peopleRDD转换而来。

[Scala] 纯文本查看 复制代码

?

val peopleDF = spark.createDataFrame(rowRDD, schema)

最后这里生成了DataFrame。其它基本重复了，不在啰嗦。

随机文章
本站知识点必读
最近更新