如何在scala中创建空白数据帧

Question

在if子句之外无法访问数据帧。如何访问if/else块外部的数据帧

需求：DataSource id SQL Server和从结构化数据准备JSON场景：基于区域值将填充数据，并将其放入主数据帧中。尝试访问if/else子句之外的数据帧时出现问题。下面是我尝试过的代码示例：

if(region == "UK") {
val dfUK = "select * from tablename"
}
dfuk.withColumnRenamed("ColumnName1","ColumnName2")


**Error: dfuk is unreachable**

Answer 1

分辨率：

1. 导入库-导入org.apache.spark.sql.DataFrame
2. 创建空白数据帧：

var outputdf: DataFrame = _
if(region == "UK")
{
val dfUK = "select * from tablename"
outputdf = dfUK 
}
outputdf.withColumnRenamed("ColumnName1","ColumnName2")

Answer 2

将其定义为表达式

val dfUK = if(region == "UK") { 
spark.sql("select * from tablename")
} //else something other definition for the df    
dfUK.withColumn...