在scala中执行如下代码，报 join 错误！！
scala> val data = itemTotalTime.join(totalTime, "userId")
错误日志如下：
<console>:29: error: overloaded method value join with alternatives:
(right: org.apache.spark.sql.Dataset[_],usingColumns: Seq[String])org.apache.spark.sql.DataFrame <and>
(right: org.apache.spark.sql.Dataset[_],usingColumn: String)org.apache.spark.sql.DataFrame
cannot be applied to (Unit, String)
val data = itemTotalTime.join(totalTime, "userId")
^
分析：应该是join的一边是DataFram 一边是Dataset 的原因，我把这两个 itemTotalTime、totalTime 都 .toDF 了一下就好了
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