Which activity allows you to fetch values that will be used in subsequent activities in an Azure Data Factory pipeline?

The activity that allows you to fetch values for use in subsequent activities within an Azure Data Factory pipeline is the Lookup activity. This activity is designed to retrieve a dataset or query results from a data source by executing a specified query or selecting data from a dataset. The values retrieved through the Lookup activity can then be stored in variables and referenced later in the pipeline, enabling dynamic workflows and data transformations based on the retrieved information.

By using Lookup, you can execute queries against databases, retrieve rows from tables, or return specific data points that may influence the flow of subsequent activities, such as conditional branching, data transformations, or further data movements. This capability makes the Lookup activity essential for scenarios where decisions must be based on data obtained from external systems or databases.

In contrast, while the Copy data activity is used to transfer data from a source to a destination, it does not inherently fetch values for later use. The Append variable activity is utilized to build on the existing values of a variable but does not retrieve new data. The Execute pipeline activity enables the invocation of another pipeline but is focused on orchestration rather than fetching data itself. Thus, the Lookup activity stands out as the appropriate choice for fetching values to be utilized later in the pipeline process.