【spark2.x】如何通过SparkSQL读取csv文件

package cn.itcast.spark.source
import java.util.Properties
import org.apache.spark.sql.types.{DoubleType, IntegerType, LongType, StructType}
import org.apache.spark.sql.{DataFrame, SparkSession}
object _03SparkSQLSourceTest {
  def main(args: Array[String]): Unit = {
    // 构建SparkSession实例对象
    val spark: SparkSession = SparkSession.builder()
      .master("local[4]")
      .appName(this.getClass.getSimpleName.stripSuffix("$"))
      .config("spark.sql.shuffle.partitions", "4")
      .getOrCreate()
    import spark.implicits._
    // TODO: 1. CSV 格式数据文本文件数据 -> 依据 CSV文件首行是否是列名称，决定读取数据方式不一样的
    /*
      CSV 格式数据：
        每行数据各个字段使用逗号隔开
        也可以指的是，每行数据各个字段使用 单一 分割符 隔开数据
     */
    // 方式一：首行是列名称，数据文件u.dat
    val dataframe: DataFrame = spark.read
      .format("csv")
      .option("sep", "\\t")
      .option("header", "true")
      .option("inferSchema", "true")
      .load("datas/ml-100k/u.dat")
    dataframe.printSchema()
    dataframe.show(10, truncate = false)
    // 方式二：首行不是列名，需要自定义Schema信息，数据文件u.data
    // 自定义schema信息
    val schema: StructType = new StructType()
      .add("user_id", IntegerType, nullable = true)
      .add("iter_id", IntegerType, nullable = true)
      .add("rating", DoubleType, nullable = true)
      .add("timestamp", LongType, nullable = true)
    val df: DataFrame = spark.read
      .format("csv")
      .schema(schema)
      .option("sep", "\\t")
      .load("datas/ml-100k/u.data")
    df.printSchema()
    df.show(10, truncate = false)
    /* ============================================================================== */
    // TODO: 2. 读取MySQL表中数据
    // 第一、简洁版格式
    /*
      def jdbc(url: String, table: String, properties: Properties): DataFrame
     */
    val props =  new Properties()
    props.put("user", "root")
    props.put("password", "123456")
    props.put("driver", "com.mysql.cj.jdbc.Driver")
    val empDF: DataFrame = spark.read.jdbc(
      "jdbc:mysql://node1.itcast.cn:3306/?serverTimezone=UTC&characterEncoding=utf8&useUnicode=true", //
      "db_test.emp", //
      props //
    )
    println(s"Partition Number = ${empDF.rdd.getNumPartitions}")
    empDF.printSchema()
    empDF.show(10, truncate = false)
    // 第二、标准格式写
    /*
      WITH tmp AS (
        select * from emp e join dept d on e.deptno = d.deptno
      )
     */
    val table: String = "(select ename,deptname,sal from db_test.emp e join db_test.dept d on e.deptno = d.deptno) AS tmp"
    val joinDF: DataFrame = spark.read
      .format("jdbc")
      .option("url", "jdbc:mysql://node1.itcast.cn:3306/?serverTimezone=UTC&characterEncoding=utf8&useUnicode=true")
      .option("driver", "com.mysql.cj.jdbc.Driver")
      .option("user", "root")
      .option("password", "123456")
      .option("dbtable", table)
      .load()
    joinDF.printSchema()
    joinDF.show(10, truncate = false)
    // 应用结束，关闭资源
    spark.stop()
  }
}