Which of the following is considered a bad practice when performing joins in PySpark?

Using right joins in PySpark is often viewed as a bad practice primarily due to performance considerations and the potential for increased complexity in your data transformations. Right joins can lead to inefficiencies, especially with large datasets. They might also introduce ambiguity when it comes to understanding the data relationships because they are less commonly utilized compared to left joins. This can make code harder to read and maintain since left joins are typically more intuitive — the first dataframe is always the driving dataset in the join operation.

In contrast, practices such as using dataframe aliases to disambiguate column names help maintain clarity, especially when two dataframes contain columns with identical names. This makes it easier to manage the resulting dataset and prevents potential errors in column references.

Explicitly specifying the join type enhances code clarity and ensures that the intended join logic is executed. This is particularly important in collaborative environments or complex workflows where the default join behavior may not suffice or could lead to unintended results.

Dropping unnecessary columns after the join is a good practice as it reduces memory usage and improves performance, streamlining the resulting dataframe for further processing. Overall, adopting a cautious approach with joins is essential to optimize performance and maintain code comprehensibility in PySpark.