1. A method of combining data, the method comprising: performing a plurality of merge operations using a single scan of a source data structure, wherein each merge operation is an operation to merge data from the source data structure into at least one of a plurality of destination data structures; wherein each of the source data structure and the destination data structures is a relational data structure; and wherein each of the merge operations includes identifying whether any differences exist between the source data structure and that destination data structure, and modifying that destination data structure based on any identified differences.