What does a Lookup transformation do?

The Lookup transformation is specifically designed to retrieve a value from a secondary dataset and append it to the primary dataset based on a matching key. This process allows users to enhance their initial dataset with additional information that resides in a different dataset, effectively enriching the data being analyzed.

When using a Lookup transformation, you essentially have two datasets: the primary (or left) dataset and the secondary (or right) dataset. The transformation searches for a specified key in the right dataset that corresponds to a key in the left dataset. Upon finding a match, it retrieves the desired value from the right dataset and attaches it to the appropriate row in the left dataset, augmenting it with relevant details. This capability is crucial for data analysis tasks where context is needed from related data sources.

In contrast, the other options describe different functionalities that do not align with what a Lookup transformation accomplishes. For instance, combining two data streams into one is typically handled by merge or join operations rather than a lookup. Adding new rows based on conditions may refer to conditional transformations or aggregations, while removing duplicates pertains to data cleaning processes, which do not have a direct connection to the lookup functionality. Thus, the choice accurately reflects the purpose and operation of a Lookup transformation in data analytics.