What operation would you perform to ensure no duplicate records appear in the results of a query?

To ensure no duplicate records appear in the results of a query, using the union operation is the correct choice. The union operation combines the results of two or more queries and automatically eliminates any duplicate records from the final output. This feature of unioning results is particularly useful when consolidating data from similar tables or datasets while maintaining the uniqueness of the records presented.

In relational database management, when multiple datasets are combined, there may be overlapping data. The union operation addresses this by identifying and discarding duplicate records seamlessly, making it easier for analysts and decision-makers to work with a clean set of data.

In contrast, the other options serve different purposes: joining combines records based on a related column, intersecting finds common records between datasets, and projecting focuses on selecting specific columns from a dataset without necessarily addressing duplicates. Thus, employing the union operation effectively meets the need to avoid duplicate records in query results.