将整数转换为日期以计算天数

可以强制转换registryDate为String类型，然后应用to_date并datediff计算天数差异，如下所示：

import org.apache.spark.sql.functions._
import org.apache.spark.sql.types._
import java.sql.Date

val df = Seq(
20130826, 20130829, 20130816, 20130825
).toDF("registryDate")

df.
withColumn("registryDate2", to_date($"registryDate".cast(StringType), "yyyyMMdd")).
withColumn("todaysDate", lit(Date.valueOf("2018-11-24"))).
withColumn("DaysInBetween", datediff($"todaysDate", $"registryDate2")).
show
// +------------+-------------+----------+-------------+
// |registryDate|registryDate2|todaysDate|DaysInBetween|
// +------------+-------------+----------+-------------+
// | 20130826| 2013-08-26|2018-11-24| 1916|
// | 20130829| 2013-08-29|2018-11-24| 1913|
// | 20130816| 2013-08-16|2018-11-24| 1926|
// | 20130825| 2013-08-25|2018-11-24| 1917|
// +------------+-------------+----------+-------------+