spark sql 操作

Posted 2020-09-14 天之涯0204

DSL风格语法

1、查看DataFrame中的内容

scala> df1.show
+---+--------+---+
| id| name|age|
+---+--------+---+
| 1|zhansgan| 16|
| 2| lisi| 18|
| 3| wangwu| 21|
| 4|xiaofang| 22|
+---+--------+---+

2、查看DataFrame部分列的数据

scala> df1.select(df1.col("name")).show
+--------+
| name|
+--------+
|zhansgan|
| lisi|
| wangwu|
|xiaofang|
+--------+

　　

scala> df1.select(col("name"), col("age")).show
+--------+---+
| name|age|
+--------+---+
|zhansgan| 16|
| lisi| 18|
| wangwu| 21|
|xiaofang| 22|
+--------+---+

 

scala> df1.select("name").show
+--------+
| name|
+--------+
|zhansgan|
| lisi|
| wangwu|
|xiaofang|
+--------+

3、查看DataFrame schema信息

scala> df1.printSchema
root
|-- id: integer (nullable = false)
|-- name: string (nullable = true)
|-- age: integer (nullable = false)

 

 

4、查询name和age并将age + 1

scala> df1.select(col("name"), col("age") + 1).show
+--------+---------+
| name|(age + 1)|
+--------+---------+
|zhansgan| 17|
| lisi| 19|
| wangwu| 22|
|xiaofang| 23|
+--------+---------+

　　

scala> df1.select(df1("name"), df1("age") + 1).show
+--------+---------+
| name|(age + 1)|
+--------+---------+
|zhansgan| 17|
| lisi| 19|
| wangwu| 22|
|xiaofang| 23|
+--------+---------+

5、过滤年龄大于20的人

scala> df1.filter(col("age") > 20).show
+---+--------+---+
| id| name|age|
+---+--------+---+
| 3| wangwu| 21|
| 4|xiaofang| 22|
+---+--------+---+

　　

6、按年龄分组，并统计年龄相同的人数

scala> df1.groupBy("age").count().show
+---+-----+ 
|age|count|
+---+-----+
| 16| 1|
| 18| 1|
| 21| 1|
| 22| 1|
+---+-----+

　　

SQL风格

在使用SQL风格前，首先需要将DataFrame注册成表

df1.registerTempTable("t_person")

 

1、查询年龄最大的前两个人

scala> sqlContext.sql("select * from t_person order by age desc limit 2").show
+---+--------+---+
| id| name|age|
+---+--------+---+
| 4|xiaofang| 22|
| 3| wangwu| 21|
+---+--------+---+

　　

2、显示表的schema信息

scala> sqlContext.sql("desc t_person").show
+--------+---------+-------+
|col_name|data_type|comment|
+--------+---------+-------+
| id| int| |
| name| string| |
| age| int| |
+--------+---------+-------+

　　

DataFrame api 操作

 

package bigdata.spark.sql

import org.apache.spark.sql.SQLContext
import org.apache.spark.{SparkContext, SparkConf}

import scala.reflect.internal.util.TableDef.Column

/**
  * Created by Administrator on 2017/4/27.
  */
object SparkSqlDemo {

  def main(args: Array[String]) {
    val conf = new SparkConf()
    conf.setAppName("SparkSqlDemo")
    conf.setMaster("local")
    val sc = new SparkContext(conf)
    val sqlContext = new SQLContext(sc)
    val rdd1 = sc.textFile("hdfs://m1:9000/persons.txt").map(_.split(" "))
    val rdd2 = rdd1.map(x => Person(x(0).toInt, x(1), x(2).toInt))

    // 导入隐式转换，里面包含了RDD隐式转换为DataFrame的方法
    import sqlContext.implicits._
    // df1现在已经是DataFrame了
    val df1 = rdd2.toDF
    df1.show


    df1.select("age").show()

    df1.select(col="age").show
    df1.select(df1.col("age")).show

    import df1._
    df1.select(col("age")).show

    df1.select(col("age") > 20).show

    df1.select(col("age") + 1).show

    df1.filter(col("age") > 20).show()


    df1.registerTempTable("t_person")

    sqlContext.sql("select * from t_person").show()

    sqlContext.sql("select * from t_person order by age desc limit 2").show()

    sc.stop()

  }

  // 这个类必须放在main方法外面，不然的话会报错
  case class Person(id:Int, name:String, age:Int)

}

　　

StructType指定Schema

package bigdata.spark.sql

import org.apache.spark.sql.types.{StringType, IntegerType, StructField, StructType}
import org.apache.spark.sql.{Row, SQLContext}
import org.apache.spark.{SparkContext, SparkConf}

import scala.reflect.internal.util.TableDef.Column

/**
  * Created by Administrator on 2017/4/27.
  */
object SparkSqlDemo {

  def main(args: Array[String]) {
    val conf = new SparkConf()
    conf.setAppName("SparkSqlDemo")
    conf.setMaster("local")
    val sc = new SparkContext(conf)
    val sqlContext = new SQLContext(sc)
    val rdd1 = sc.textFile("hdfs://m1:9000/persons.txt").map(_.split(" "))
    val rdd2 = rdd1.map(x => Row(x(0).toInt, x(1), x(2).toInt))
    // 创建schema
    val schema = StructType(
      List(
        // 名称 类型 是否可以为空
        StructField("id", IntegerType, false),
        StructField("name", StringType, false),
        StructField("age", IntegerType, false)
      )
    )

    // 创建DataFrame
    val df1 = sqlContext.createDataFrame(rdd2, schema)

    df1.registerTempTable("t_person")

    sqlContext.sql("select * from t_person").show()

    sc.stop()

  }

}