cast(NULL as smallint) 你必须做。。。这将把null转换为 short 键入如下架构所示。

val df1 =spark.sql(
     " select 1 as column1 , 2 column2 , cast(NULL as smallint) as column3 from table  ")
  df1.show
df1.printSchema()

结果：

+-------+-------+-------+
|column1|column2|column3|
+-------+-------+-------+
|      1|      2|   null|
+-------+-------+-------+

root
 |-- column1: integer (nullable = false)
 |-- column2: integer (nullable = false)
 |-- column3: short (nullable = true)

另一方面，它将是nulltype而不是small int类型。。

val df1 =spark.sql(" select 1 as column1 , 2 column2 ,  NULL   as column3 from table  ")
  df1.show
df1.printSchema()

+-------+-------+-------+
|column1|column2|column3|
+-------+-------+-------+
|      1|      2|   null|
+-------+-------+-------+

root
 |-- column1: integer (nullable = false)
 |-- column2: integer (nullable = false)
 |-- column3: null (nullable = true)

这就是你得到例外的原因。