如何打印出spark.sql对象？

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我有一个spark.sql对象，其中包含几个变量。

import com.github.nscala_time.time.Imports.LocalDate

val first_date = new LocalDate(2020, 4, 1)
val second_date = new LocalDate(2020, 4, 7)

val mydf = spark.sql(s"""
        select *
        from tempView
        where timestamp between '{0}' and '{1}'
""".format(start_date.toString, end_date.toString))

I want to print out mydf because I ran mydf.count and got 0 as the outcome.

I ran mydf and got back mydf: org.apache.spark.sql.DataFrame = [column: type]

I also tried println(mydf) and it didn't return the query.

There is this related question, but it does not have the answer.

如何打印查询？