What is a necessary step before applying the delta transformation?

The necessary step before applying the delta transformation is sorting the data. Sorting is essential because the delta transformation aims to track changes or differences between sequential data points. To accurately compute the differences or identify changes, the data must be in a predefined order. If the data is not sorted, the transformation may yield incorrect results, as it could misinterpret which data corresponds to which timeframe or grouping.

In contrast, adding new columns, removing duplicates, and filtering irrelevant fields, while potentially useful steps in data preparation, do not fundamentally support the delta transformation process specifically. These steps might be needed for other aspects of data management but do not ensure that the comparisons made in a delta transformation are valid, hence making sorting the primary prerequisite.