in/exists predicate 子查询只能在spark中的筛选器中使用。
以下操作在本地重新创建的数据副本中起作用：

select orderid, custid, case when existing_customer is null then 'N' else 'Y' end existing_customer
          from (select o.orderid, o.custid, c.custid existing_customer
                from orders o
                left join customer c
                 on c.custid = o.custid)

以下是它如何处理重新创建的数据：

def textToView(csv: String, viewName: String) = {
   spark.read
  .option("ignoreLeadingWhiteSpace", "true")
  .option("ignoreTrailingWhiteSpace", "true")
  .option("delimiter", "|")
  .option("header", "true")
  .csv(spark.sparkContext.parallelize(csv.split("\n")).toDS)
  .createOrReplaceTempView(viewName)
}

textToView("""id | custid
              1  | XYZ
              2  | UVW""", "customer")

textToView("""orderid | custid
              12345   | XYZ
              34566   | XYZ
              68790   | MNP
              59876   | QRS
              15620   | UVW""", "orders")

spark.sql("""
          select orderid, custid, case when existing_customer is null then 'N' else 'Y' end existing_customer
          from (select o.orderid, o.custid, c.custid existing_customer
                from orders o
                left join customer c
                 on c.custid = o.custid)""").show

返回：

+-------+------+-----------------+
|orderid|custid|existing_customer|
+-------+------+-----------------+
|  59876|   QRS|                N|
|  12345|   XYZ|                Y|
|  34566|   XYZ|                Y|
|  68790|   MNP|                N|
|  15620|   UVW|                Y|
+-------+------+-----------------+