Practice reading query plans 2

Three dataframes are available: part2_df, part3_df, and part4_df. The questions posed in this exercise can be answered by inspecting the explain() output of each dataframe.

Note that Spark tags each column name with a descriptor, delimited by a # symbol. For example, word#0, id#1L, part#2, and title#3. For the purpose of this exercise, these descriptors can be ignored.