Which of the following query optimization techniques involves examining only the data that is needed for a particular task?

Making a temporary table can sometimes help in breaking down complex queries, but it doesn't primarily describe the technique of "examining only the data that is needed" in the most direct sense of retrieval optimization.

Creating a flat file is a data storage format, not a query optimization technique for existing structured data.

Indexing documents or database tables creates a data structure that improves the speed of data retrieval operations on a database table or collection. By creating an index on relevant columns, the database can rapidly pinpoint the exact rows or documents that match a query's criteria, thus avoiding a full table or document scan and retrieving only the necessary data.

Creating an execution plan is the database engine's internal process for determining the most efficient way to execute a query; it's an output of optimization, not an optimization technique itself.