我需要在foreach循环中使用各种SELECT语句迭代DF的内容,将输出写入文本文件.foreach循环中的任何SELECT语句都返回NullPointerException.我无法理解为什么会这样."for"循环内的SELECT语句不会返回此错误.
这是测试用例.
// step 1 of 6: create the table and load two rows
vc.sql(s"""CREATE TEMPORARY TABLE TEST1 (
c1 varchar(4)
,username varchar(5)
,numeric integer) USING com.databricks.spark.csv OPTIONS (path "/tmp/test.txt")""")
// step 2 of 6: confirm that the data is queryable
vc.sql("SELECT * FROM TEST1").show()
+----+--------+-------+
| c1|username|numeric|
+----+--------+-------+
|col1| USER1| 0|
|col1| USER2| 1|
+----+--------+-------+
// Step 3 of 6: create a dataframe for the table
var df=vc.sql("""SELECT * FROM TEST1""")
// step 4 of 6: create a second …