Reproduces first query in https://databricks.com/blog/2016/02/09/reshaping-data-with-pivot-in-apache-spark.html

ReshapingDataWithPivotInSparkArticle.scala

import gallia._
import aptus._ // for divideBy and significantFigures utilities

// ===========================================================================
object ReshapingDataWithPivotInSparkArticle {
  // reproduces first query in https://databricks.com/blog/2016/02/09/reshaping-data-with-pivot-in-apache-spark.html
  
  // ---------------------------------------------------------------------------
  // t210224102310 - not actually implemented yet, but will also use
  //   https://github.com/galliaproject/gallia-core/blob/init/src/main/scala/gallia/atoms/AtomsIX.scala#L110 for local runs
  implicit class Connection_(u: java.sql.Connection) { def stream(tableName: String): HeadZ = HeadZ.Dummy }

  val conn: java.sql.Connection = null
  
  // ===========================================================================
  def main(args: Array[String]): Unit = {

    /*
      sql("""select *, concat('Q', d_qoy) as qoy
        from store_sales
        join date_dim on ss_sold_date_sk = d_date_sk
        join item on ss_item_sk = i_item_sk""")
        .groupBy("i_category")
        .pivot("qoy")
        .agg(round(sum("ss_sales_price")/1000000,2))
        .show)
     */

    // ---------------------------------------------------------------------------    
    // note: not tested (TODO: t210224102851)

    conn // "jdbc://.../"
      .stream("store_sales")
        .generate("qoy").from("Q", "d_qoy").using(_ + " " + _)
        .innerJoin(
          conn.stream("date_dim") -> ("ss_sold_date_sk" <~> "d_date_sk"),
          conn.stream("item")     -> ("ss_item_sk"      <~> "i_item_sk"))
        .pivot(_.double("ss_sales_price"))
          .using { _.sum.divideBy(1000000).significantFigures(2) /* uses aptus utils */ }
            .rows("i_category")
              .column("qoy").asNewKeys("Q1", "Q2", "Q3", "Q4")
      .printJsonl()
  }

}

// ===========================================================================

changed columns to column to reflect t210303101932 (commit 719bcfd)