Scala 加入不同的数据集以获取一列的值

Question

I am new to Scala. I now have 3 tables.

A:

Marketplace	Level	Band
US	LEVEL_1
CA	LEVEL_1	BAND_1

B:

Marketplace	Level	Value
US	LEVEL_1	10

C:

Marketplace	Level	Band	Value
CA	LEVEL_1	BAND_1	20

I would want to:

For rows with marketplace = US in table A -> join table B on Seq(Marketplace, Level) to get the Value;

For rows with marketplace = CA in table A -> join table C on Seq(Marketplace, Level, Band) to get the Value.

The output table will be like:

Marketplace	Level	Band	Value
US	LEVEL_1		10
CA	LEVEL_1	BAND_1	20

How should I write Scala code to achieve this? Thanks!

Answer 1

import org.apache.spark.sql.SparkSession
import org.apache.spark.sql.functions.{coalesce, col}
import spark.implicits._
val A = Seq(("US", "LEVEL_1", ""), ("CA", "LEVEL_1", "BAND_1"))
  .toDF("Marketplace", "Level", "Band")
val B = Seq(("US", "LEVEL_1", 10)).toDF("Marketplace", "Level", "Value")
val C = Seq(("CA", "LEVEL_1", "BAND_1", 20)).toDF(
  "Marketplace",
  "Level",
  "Band",
  "Value"
)

val res = A
  .join(B, A.col("Marketplace") === B.col("Marketplace"), "left")
  .join(C, A.col("Marketplace") === C.col("Marketplace"), "left")
  .select(
    A.col("Marketplace").alias("Marketplace"),
    A.col("Level").alias("Level"),
    C.col("Band").alias("Band"),
    coalesce(B.col("Value"), C.col("Value")).alias("Value")
  )

res.show(false)
//    +-----------+-------+------+-----+
//    |Marketplace|Level  |Band  |Value|
//    +-----------+-------+------+-----+
//    |US         |LEVEL_1|null  |10   |
//    |CA         |LEVEL_1|BAND_1|20   |
//    +-----------+-------+------+-----+