1. A method of combining data within a database system, the method comprising: performing a scan of a source data structure to obtain source data; performing a first merge operation to merge the source data into a first destination data structure; storing one or more changes to the first destination data structure in an intermediate data structure; using the intermediate data structure to determine whether the source data should be augmented with the one or more changes; and performing one or more subsequent merge operations using the source data without performing another scan of the source data structure.