为创建所需的值 stack 动态&在需要的地方使用它。请检查下面的代码以生成相同的动态值。

scala> val js = Seq("""{"1": "a", "2": "b","3":"c","4":"d","5":"e"}""").toDS
js: org.apache.spark.sql.Dataset[String] = [value: string]

scala> val df = spark.read.json(js)
df: org.apache.spark.sql.DataFrame = [1: string, 2: string ... 3 more fields]

scala> val stack = s"""stack(${df.columns.max},${df.columns.flatMap(c => Seq(s"'${c}'",s"`${c}`")).mkString(",")}) as (id,name)"""
exprC: String = stack(5,'1',`1`,'2',`2`,'3',`3`,'4',`4`,'5',`5`) as (id,name)

scala> df.select(expr(stack)).show(false)
+---+----+
|id |name|
+---+----+
|1  |a   |
|2  |b   |
|3  |c   |
|4  |d   |
|5  |e   |
+---+----+

scala> spark.sql(s"""select ${stack} from table """).show(false)
+---+----+
|id |name|
+---+----+
|1  |a   |
|2  |b   |
|3  |c   |
|4  |d   |
|5  |e   |
+---+----+

scala>
``` `Updated Code to fetch data from json file` ```
scala> "hdfs dfs -cat /tmp/sample.json".!
{"1": "a", "2": "b","3":"c","4":"d","5":"e"}
res4: Int = 0

scala> val df = spark.read.json("/tmp/sample.json")
df: org.apache.spark.sql.DataFrame = [1: string, 2: string ... 3 more fields]

scala> val stack = s"""stack(${df.columns.max},${df.columns.flatMap(c => Seq(s"'${c}'",s"`${c}`")).mkString(",")}) as (id,name)"""
stack: String = stack(5,'1',`1`,'2',`2`,'3',`3`,'4',`4`,'5',`5`) as (id,name)

scala> df.select(expr(stack)).show(false)
+---+----+
|id |name|
+---+----+
|1  |a   |
|2  |b   |
|3  |c   |
|4  |d   |
|5  |e   |
+---+----+

scala> df.createTempView("table")

scala> spark.sql(s"""select ${stack} from table """).show(false)
+---+----+
|id |name|
+---+----+
|1  |a   |
|2  |b   |
|3  |c   |
|4  |d   |
|5  |e   |
+---+----+